An 'Export to Excel' button on a datagrid form triggers the following error when pressed: 2012-07-30 13:49:18.294 ERROR Connectororg.json.JSONException: JSONObject["buttonid"] not found. at org.json.JSONObject.get(JSONObject.java:511) at org.json.JSONObject.getLong(JSONObject.java:650) at ew.execute(SourceFile:83) at jB.a(SourceFile:304) at jB.a(SourceFile:233) at jB.processRequest(SourceFile:177) at fM.a(SourceFile:71) at com.mendix.core.MxRuntime.processRequest(SourceFile:946) at com.mendix.m2ee.server.handler.RuntimeHandler.handle(RuntimeHandler.java:42) 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:619) All other parts of the application work flawlessly, as far as I can see. This error does NOT occur if I run the application via http://servername:8080 (which is the defined port for the application). But the error DOES occur if I run the application via http://www.allesmag.nl/index.html or http://servername:80 (which are handled by IIS first) It seems the error was introduced when I switched from developer version 2.5.1 to 2.5.8 recently. If it would have occurred earlier I think I would have known. But I'm not sure of that. Any ideas?