You probably jump from A to B to C and back to A or created other kind of loops in your questionnaire. E.g. Dependencies in conditions between questions with loops.
I also have a StackOverflowError. Any kind of help is welcome.
An unhandled error occurred in the MxRuntime.
java.lang.StackOverflowError at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632) at java.lang.ClassLoader.defineClass(ClassLoader.java:616) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141) at java.net.URLClassLoader.defineClass(URLClassLoader.java:283) at java.net.URLClassLoader.access$000(URLClassLoader.java:58) at java.net.URLClassLoader$1.run(URLClassLoader.java:197) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:248) at mf.a(SourceFile:231) at mf.a(SourceFile:197) at mf.a(SourceFile:94) at me.executeAction(SourceFile:101) at com.mendix.systemwideinterfaces.core.UserAction.execute(SourceFile:57) at com.mendix.core.actionmanagement.CoreAction.call(SourceFile:457) at hC.b(SourceFile:182) at com.mendix.core.Core.executeSync(SourceFile:196) at hH.e(SourceFile:102) at hH.a(SourceFile:50) at hE.execute(SourceFile:99) at etc etc