What does this error mean?

[dornus]

I keep getting this and don't know why. It doesn't show any of my custom classes in the stacktrace so I assume it has something to do with JBoss?

java.lang.IllegalStateException
 at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:404)
 at org.apache.catalina.servlets.DefaultServlet.serveResource(DefaultServlet.java:695)
 at org.apache.catalina.servlets.DefaultServlet.doGet(DefaultServlet.java:348)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:697)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
 at org.jboss.web.tomcat.security.CustomPrincipalValve.invoke(CustomPrincipalValve.java:39)
 at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:159)
 at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:59)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
 at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:868)
 at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:663)
 at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
 at org.apache.tomcat.util.net.MasterSlaveWorkerThread.run(MasterSlaveWorkerThread.java:112)
 at java.lang.Thread.run(Thread.java:595)