You should upgrade to a newer beta version (beta 2 for example)
Same problem here. I'm using Mendix Runtime Version: 2.5-beta - 25
Mendix.M2EE.M2EEException: Request <{"action":"start","params":{"mxslotname":"default"}}> failed: {"type":"exception","description":"An exception occurred in request '{\"action\":\"start\",\"params\":{}}'An exception occurred while running the after-startup-action, An exception occurred while running the after-startup-action\n\tat com.mendix.core.CoreManager.c(SourceFile:360)\n\tat lx.execute(SourceFile:43)\n\tat dw.processRequest(SourceFile:116)\n\tat fA.a(SourceFile:58)\n\tat com.mendix.core.CoreManager.processRequest(SourceFile:717)\n\tat com.mendix.m2ee.api.M2EEContextImpl.processRequest(M2EEContextImpl.java:74)\n\tat com.mendix.m2ee.server.servlet.AdminServlet.rerouteRuntimeAdminRequest(AdminServlet.java:184)\n\tat com.mendix.m2ee.server.servlet.AdminServlet.doPost(AdminServlet.java:126)\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:727)\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:820)\n\tat org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:530)\n\tat org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:427)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)\n\tat org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:494)\n\tat org.eclipse.jetty.server.session.SessionHandler.handle(SessionHandler.java:182)\n\tat org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:933)\n\tat org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:362)\n\tat org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:867)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)\n\tat org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:113)\n\tat org.eclipse.jetty.server.Server.handle(Server.java:334)\n\tat org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:559)\n\tat org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:992)\n\tat org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:550)\n\tat org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:203)\n\tat org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:406)\n\tat org.eclipse.jetty.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:462)\n\tat org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:436)\n\tat java.lang.Thread.run(Thread.java:619)\n\nCaused by:\ncom.mendix.core.CoreException: com.mendix.core.CoreException: java.lang.IllegalArgumentException: Action should not be null\n\tat il.b(SourceFile:165)\n\tat com.mendix.core.CoreManager.c(SourceFile:358)\n\tat lx.execute(SourceFile:43)\n\tat dw.processRequest(SourceFile:116)\n\tat fA.a(SourceFile:58)\n\tat com.mendix.core.CoreManager.processRequest(SourceFile:717)\n\tat com.mendix.m2ee.api.M2EEContextImpl.processRequest(M2EEContextImpl.java:74)\n\tat com.mendix.m2ee.server.servlet.AdminServlet.rerouteRuntimeAdminRequest(AdminServlet.java:184)\n\tat com.mendix.m2ee.server.servlet.AdminServlet.doPost(AdminServlet.java:126)\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:727)\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:820)\n\tat org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:530)\n\tat org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:427)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)\n\tat org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:494)\n\tat org.eclipse.jetty.server.session.SessionHandler.handle(SessionHandler.java:182)\n\tat org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:933)\n\tat org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:362)\n\tat org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:867)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)\n\tat org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:113)\n\tat org.eclipse.jetty.server.Server.handle(Server.java:334)\n\tat org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:559)\n\tat org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:992)\n\tat org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:550)\n\tat org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:203)\n\tat org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:406)\n\tat org.eclipse.jetty.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:462)\n\tat org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:436)\n\tat java.lang.Thread.run(Thread.java:619)\n\nCaused by:\ncom.mendix.core.CoreException: java.lang.IllegalArgumentException: Action should not be null\n\tat il.b(SourceFile:165)\n\tat com.mendix.core.Core.executeSync(SourceFile:158)\n\tat ei.h(SourceFile:72)\n\tat ei.a(SourceFile:34)\n\tat da.execute(SourceFile:105)\n\tat com.mendix.core.actionmanagement.CoreAction.call(SourceFile:417)\n\tat il.b(SourceFile:160)\n\tat com.mendix.core.CoreManager.c(SourceFile:358)\n\tat lx.execute(SourceFile:43)\n\tat dw.processRequest(SourceFile:116)\n\tat fA.a(SourceFile:58)\n\tat com.mendix.core.CoreManager.processRequest(SourceFile:717)\n\tat com.mendix.m2ee.api.M2EEContextImpl.processRequest(M2EEContextImpl.java:74)\n\tat com.mendix.m2ee.server.servlet.AdminServlet.rerouteRuntimeAdminRequest(AdminServlet.java:184)\n\tat com.mendix.m2ee.server.servlet.AdminServlet.doPost(AdminServlet.java:126)\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:727)\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:820)\n\tat org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:530)\n\tat org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:427)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)\n\tat org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:494)\n\tat org.eclipse.jetty.server.session.SessionHandler.handle(SessionHandler.java:182)\n\tat org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:933)\n\tat org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:362)\n\tat org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:867)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)\n\tat org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:113)\n\tat org.eclipse.jetty.server.Server.handle(Server.java:334)\n\tat org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:559)\n\tat org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:992)\n\tat org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:550)\n\tat org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:203)\n\tat org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:406)\n\tat org.eclipse.jetty.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:462)\n\tat org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:436)\n\tat java.lang.Thread.run(Thread.java:619)\n\nCaused by:\njava.lang.IllegalArgumentException: Action should not be null\n\tat com.mendix.core.Core.execute(SourceFile:187)\n\tat gX.a(SourceFile:63)\n\tat kK.a(SourceFile:69)\n\tat eL.executeAction(SourceFile:93)\n\tat com.mendix.systemwideinterfaces.core.UserAction.execute(SourceFile:49)\n\tat com.mendix.core.actionmanagement.CoreAction.call(SourceFile:417)\n\tat il.b(SourceFile:156)\n\tat com.mendix.core.Core.executeSync(SourceFile:158)\n\tat ei.h(SourceFile:72)\n\tat ei.a(SourceFile:34)\n\tat da.execute(SourceFile:105)\n\tat com.mendix.core.actionmanagement.CoreAction.call(SourceFile:417)\n\tat il.b(SourceFile:160)\n\tat com.mendix.core.CoreManager.c(SourceFile:358)\n\tat lx.execute(SourceFile:43)\n\tat dw.processRequest(SourceFile:116)\n\tat fA.a(SourceFile:58)\n\tat com.mendix.core.CoreManager.processRequest(SourceFile:717)\n\tat com.mendix.m2ee.api.M2EEContextImpl.processRequest(M2EEContextImpl.java:74)\n\tat com.mendix.m2ee.server.servlet.AdminServlet.rerouteRuntimeAdminRequest(AdminServlet.java:184)\n\tat com.mendix.m2ee.server.servlet.AdminServlet.doPost(AdminServlet.java:126)\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:727)\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:820)\n\tat org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:530)\n\tat org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:427)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)\n\tat org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:494)\n\tat org.eclipse.jetty.server.session.SessionHandler.handle(SessionHandler.java:182)\n\tat org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:933)\n\tat org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:362)\n\tat org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:867)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)\n\tat org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:113)\n\tat org.eclipse.jetty.server.Server.handle(Server.java:334)\n\tat org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:559)\n\tat org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:992)\n\tat org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:550)\n\tat org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:203)\n\tat org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:406)\n\tat org.eclipse.jetty.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:462)\n\tat org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:436)\n\tat java.lang.Thread.run(Thread.java:619)\n\nCaused by:\nAction should not be null\n\tat il.b(SourceFile:148)\n\tat com.mendix.core.Core.execute(SourceFile:180)\n\tat gX.a(SourceFile:63)\n\tat kK.a(SourceFile:69)\n\tat eL.executeAction(SourceFile:93)\n\tat com.mendix.systemwideinterfaces.core.UserAction.execute(SourceFile:49)\n\tat com.mendix.core.actionmanagement.CoreAction.call(SourceFile:417)\n\tat il.b(SourceFile:156)\n\tat com.mendix.core.Core.executeSync(SourceFile:158)\n\tat ei.h(SourceFile:72)\n\tat ei.a(SourceFile:34)\n\tat da.execute(SourceFile:105)\n\tat com.mendix.core.actionmanagement.CoreAction.call(SourceFile:417)\n\tat il.b(SourceFile:160)\n\tat com.mendix.core.CoreManager.c(SourceFile:358)\n\tat lx.execute(SourceFile:43)\n\tat dw.processRequest(SourceFile:116)\n\tat fA.a(SourceFile:58)\n\tat com.mendix.core.CoreManager.processRequest(SourceFile:717)\n\tat com.mendix.m2ee.api.M2EEContextImpl.processRequest(M2EEContextImpl.java:74)\n\tat com.mendix.m2ee.server.servlet.AdminServlet.rerouteRuntimeAdminRequest(AdminServlet.java:184)\n\tat com.mendix.m2ee.server.servlet.AdminServlet.doPost(AdminServlet.java:126)\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:727)\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:820)\n\tat org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:530)\n\tat org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:427)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)\n\tat org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:494)\n\tat org.eclipse.jetty.server.session.SessionHandler.handle(SessionHandler.java:182)\n\tat org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:933)\n\tat org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:362)\n\tat org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:867)\n\tat org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)\n\tat org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:113)\n\tat org.eclipse.jetty.server.Server.handle(Server.java:334)\n\tat org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:559)\n\tat org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:992)\n\tat org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:550)\n\tat org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:203)\n\tat org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:406)\n\tat org.eclipse.jetty.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:462)\n\tat org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:436)\n\tat java.lang.Thread.run(Thread.java:619)\n","result":560} ---> System.Net.WebException: The remote server returned an error: (560) 560.
at System.Net.HttpWebRequest.GetResponse()
at Mendix.M2EE.M2EEClient.DoHttpRequest(String json, Int32 timeout) in c:\cygwin\home\autobuild\tmp\build2-2.5\src\Mendix.M2EE\M2EEClient.cs:line 192
--- End of inner exception stack trace ---
at Mendix.M2EE.M2EEClient.DoHttpRequest(String json, Int32 timeout) in c:\cygwin\home\autobuild\tmp\build2-2.5\src\Mendix.M2EE\M2EEClient.cs:line 200
at Mendix.M2EE.M2EEClient.ExecuteAction(M2EEAction action, Int32 timeout) in c:\cygwin\home\autobuild\tmp\build2-2.5\src\Mendix.M2EE\M2EEClient.cs:line 156
at Mendix.M2EE.M2EEClient.ExecuteAction(M2EEAction action) in c:\cygwin\home\autobuild\tmp\build2-2.5\src\Mendix.M2EE\M2EEClient.cs:line 139
at Mendix.M2EE.MxSlot.Start() in c:\cygwin\home\autobuild\tmp\build2-2.5\src\Mendix.M2EE\MxSlot.cs:line 135
at Mendix.M2EE.MxSlotControl.<>c__DisplayClass3.<PerformStartup>b__2() in c:\cygwin\home\autobuild\tmp\build2-2.5\src\Mendix.M2EE\MxSlotControl.cs:line 76
at Mendix.M2EE.Background.<>c__DisplayClass5.<Do>b__3(Object s, DoWorkEventArgs e) in c:\cygwin\home\autobuild\tmp\build2-2.5\src\Mendix.M2EE\Background.cs:line 20
at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)