Tip for developers working with Mendix 3.x and Mendix 4.0 on one machine

This afternoon I decided to download and play with Mendix 4.0 since I had gotten very curious about the new features and the new mobile modeler. When I switched back to my Mendix 3.2.1 project, I had a very unpleasant surprise waiting for me. Suddenly I had trouble in every window that contains a horizontal split pane with a datagrid on the left and a dataview on the right with a listen target set to the datagrid. Every time I clicked on a row in the datagrid, I got the error message: " An error has occurred while handling the request " The console showed the following stack trace every time this error occurred: java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Number at gr.a(SourceFile:165) at gr.execute(SourceFile:120) at iI.a(SourceFile:311) at iI.a(SourceFile:240) at iI.processRequest(SourceFile:179) at iL.a(SourceFile:71) at com.mendix.core.MxRuntime.processRequest(SourceFile:856) at com.mendix.m2ee.server.handler.RuntimeHandler.handle(RuntimeHandler.java:43) at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:113) at org.eclipse.jetty.server.Server.handle(Server.java:334) at org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:559) at org.eclipse.jetty.server.HttpConnection$RequestHandler.content(HttpConnection.java:1007) at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:747) at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:209) at org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:406) at org.eclipse.jetty.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:462) at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:436) at java.lang.Thread.run(Thread.java:662) I won't tire you with all the things I tried to find out what the problem was. What I can say is that if you run into this situation and get this error message, try to clean your browser cache. Chances are high the error message will disappear.
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