IllegalStateException. Why?

Hi, I have a page which renders different panels depending on user input. Everything works fine on the initial go around however when i leave that page and then come back to it i get the following exception and i have no idea why or what it means.

phase(RESTORE_VIEW 1,com.sun.faces.context.FacesContextImpl@289875) threw exception: java.lang.IllegalStateExceptionnull

org.apache.coyote.tomcat5.CoyoteResponseFacade.sendError(CoyoteResponseFacade.java:406)

org.apache.shale.remoting.impl.AbstractResourceProcessor.sendNotModified(AbstractResourceProcessor.java:528)

org.apache.shale.remoting.impl.AbstractResourceProcessor.process(AbstractResourceProcessor.java:107)

org.apache.shale.remoting.faces.RemotingPhaseListener.afterPhase(RemotingPhaseListener.java:102)

com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:278)

com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:117)

com.sun.faces.extensions.avatar.lifecycle.PartialTraversalLifecycle.execute(PartialTraversalLifecycle.java:80)

javax.faces.webapp.FacesServlet.service(FacesServlet.java:244)

org.apache.catalina.core.ApplicationFilterChain.servletService(ApplicationFilterChain.java:398)

org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)

org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:185)

com.sun.webui.jsf.util.UploadFilter.doFilter(UploadFilter.java:240)

org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:217)

org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:185)

org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275)

org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:255)

org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:188)

org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:611)

org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:564)

com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:81)

org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:207)

org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:611)

org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:564)

org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:558)

org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1067)

org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:137)

org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:611)

org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:564)

org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:558)

org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1067)

org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:249)

com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.invokeAdapter(DefaultProcessorTask.java:618)

com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.doProcess(DefaultProcessorTask.java:549)

com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.process(DefaultProcessorTask.java:790)

com.sun.enterprise.web.connector.grizzly.DefaultReadTask.executeProcessorTask(DefaultReadTask.java:326)

com.sun.enterprise.web.connector.grizzly.DefaultReadTask.doTask(DefaultReadTask.java:248)

com.sun.enterprise.web.connector.grizzly.DefaultReadTask.doTask(DefaultReadTask.java:199)

com.sun.enterprise.web.connector.grizzly.TaskBase.run(TaskBase.java:252)

com.sun.enterprise.web.connector.grizzly.ssl.SSLWorkerThread.run(SSLWorkerThread.java:93)

phase(RESTORE_VIEW 1,com.sun.faces.context.FacesContextImpl@8f2e81) threw exception: java.lang.IllegalStateExceptionnull