Strange log error

This morning I found a new error in the log files I could not explain. I talked with the user about what the person did, but this error was generated after viewing a form with detailed views of some references. The user did not change anything but only tried to view the references. There are no microflows on this form only a main object with some different reference sets. From the log it looks like some kind of a firewall problem but I can not relate it to what the user was doing in the application. Anybody a guess about what could have been happening here? Regards, Ronald Connector: (1/30) com.mendix.core.CoreException: Exception occurred in action '[ChangeAction:: Context:Context::[Session [1bbaa0fa-9f0c-41e7-a270-82caa0f5b442]], Changes:{Facturen.Factuur_Deskundig_Medewerker_Relatie="indexOf",281474976711606, Facturen.Factuur_Gebruikers="indexOf",281474976711606}', all database changes executed by this action were rolled back Connector: (2/30) at com.mendix.core.actionmanagement.CoreAction.d(SourceFile:553) Connector: (3/30) Caused by: java.lang.IllegalArgumentException: Global identifier should be a number (given value: "indexOf") Connector: (4/30) at ay.<init>(SourceFile:93) Connector: (5/30) at com.mendix.core.objectmanagement.member.MendixObjectReferenceSet.getValueFromString(SourceFile:289) Connector: (6/30) at com.mendix.core.objectmanagement.member.MendixObjectReferenceSet.getValueFromString(SourceFile:31) Connector: (7/30) at hP.a(SourceFile:291) Connector: (8/30) at hP.a(SourceFile:106) Connector: (9/30) at hP.executeAction(SourceFile:52) Connector: (10/30) at com.mendix.systemwideinterfaces.core.UserAction.execute(SourceFile:49) Connector: (11/30) at Connector: (13/30) at com.mendix.core.Core.change(SourceFile:529) Connector: (14/30) at eR.execute(SourceFile:57) Connector: (15/30) at jx.a(SourceFile:299) Connector: (16/30) at jx.a(SourceFile:230) Connector: (17/30) at jx.processRequest(SourceFile:174) Connector: (18/30) at fI.a(SourceFile:71) Connector: (19/30) at com.mendix.core.MxRuntime.processRequest(SourceFile:938) Connector: (20/30) at com.mendix.m2ee.server.handler.RuntimeHandler.handle( Connector: (21/30) at org.eclipse.jetty.server.handler.HandlerWrapper.handle( Connector: (22/30) at org.eclipse.jetty.server.Server.handle( Connector: (23/30) at org.eclipse.jetty.server.HttpConnection.handleRequest( Connector: (24/30) at org.eclipse.jetty.server.HttpConnection$RequestHandler.content( Connector: (25/30) at org.eclipse.jetty.http.HttpParser.parseNext( Connector: (26/30) at org.eclipse.jetty.http.HttpParser.parseAvailable( Connector: (27/30) at org.eclipse.jetty.server.HttpConnection.handle( Connector: (28/30) at org.eclipse.jetty.server.nio.BlockingChannelConnector$ Connector: (29/30) at org.eclipse.jetty.util.thread.QueuedThreadPool$ Connector: (30/30) at
1 answers

I can't explain this either, from what I can gather from the stacktrace it does seem the client sent a Change request in the wrong format.