Google App Engine 500 Error

Question

Google Web Toolkit

I'm using GWT 2.6. Deploy pam from netbins. Ajax request gets 500 error. How to fix it?
Log:

EXCEPTION 
java.lang.IllegalArgumentException
  at com.google.appengine.runtime.Request.process-d8b3db063a6948af(Request.java)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:360)
  at org.mortbay.util.Loader.loadClass(Loader.java:91)
  at org.mortbay.util.Loader.loadClass(Loader.java:71)
  at org.mortbay.jetty.servlet.Holder.doStart(Holder.java:73)
  at org.mortbay.jetty.servlet.ServletHolder.doStart(ServletHolder.java:242)
  at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
  at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:685)
  at org.mortbay.jetty.servlet.Context.startContext(Context.java:140)
  at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1250)
  at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:517)
  at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:467)
  at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
  at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:437)
  at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:444)
  at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:188)
  at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:308)
  at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:300)
  at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:441)
  at java.lang.Thread.run(Thread.java:724)
E 2014-04-10 16:10:13.500
javax.servlet.ServletContext log: unavailable
javax.servlet.UnavailableException
  at org.mortbay.jetty.servlet.Holder.doStart(Holder.java:79)
  at org.mortbay.jetty.servlet.ServletHolder.doStart(ServletHolder.java:242)
  at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
  at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:685)
  at org.mortbay.jetty.servlet.Context.startContext(Context.java:140)
  at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1250)
  at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:517)
  at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:467)
  at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
  at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.createHandler(AppVersionHandlerMap.java:219)
  at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.getHandler(AppVersionHandlerMap.java:194)
  at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:134)
  at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:446)
  at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:437)
  at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:444)
  at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:188)
  at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:308)
  at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:300)
  at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:441)
  at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
  at java.lang.Thread.run(Thread.java:724)
W 2014-04-10 16:10:13.503
Failed startup of context [email protected]13cef28{/,/base/data/home/apps/s~botrunning/2.375050313455097392}
java.lang.NullPointerException
  at java.lang.Class.isAssignableFrom(Native Method)
  at org.mortbay.jetty.servlet.ServletHolder.doStart(ServletHolder.java:256)
  at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
  at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:685)
  at org.mortbay.jetty.servlet.Context.startContext(Context.java:140)
  at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1250)
  at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:517)
  at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:467)
  at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
  at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.createHandler(AppVersionHandlerMap.java:219)
  at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.getHandler(AppVersionHandlerMap.java:194)
  at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:134)
  at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:446)
  at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:437)
  at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:444)
  at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:188)
  at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:308)
  at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:300)
  at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:441)
  at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
  at java.lang.Thread.run(Thread.java:724)
C 2014-04-10 16:10:13.507
Uncaught exception from servlet
javax.servlet.UnavailableException: Initialization failed.
  at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.createHandler(AppVersionHandlerMap.java:228)
  at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.getHandler(AppVersionHandlerMap.java:194)
  at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:134)
  at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:446)
  at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:437)
  at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:444)
  at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:188)
  at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:308)
  at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:300)
  at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:441)
  at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
  at java.lang.Thread.run(Thread.java:724)
I 2014-04-10 16:10:13.509
This request caused a new process to be started for your application, and thus caused your application code to be loaded for the first time. This request may thus take longer and use more CPU than a typical request for your application.