Troubleshooting java.lang.IllegalStateException: Context is already active - jsf

Question

In a JSF 2.1 Project I am using Primefaces 5.2.
It is deployed on a Glasfish 3.1.2.2
Problem:
I´ve got the problem, that I am getting a
java.lang.IllegalStateException: Context is already active
sometimes, when I am doing a refresh page or a page redirect.
I do know, that sometimes is not a very good definition of software behaviour, but i can not really reproduce the error, it seems to appear random, to me.
Question:
Hence, I have not really found too much on the web about the cause of that kind of Exception im wondering what circumstances can produce it?
Full Trace:
[#|2015-11-10T12:51:30.246+0100|WARNING|oracle-glassfish3.1.2|javax.enterprise.system.container.web.com.sun.enterprise.web|_ThreadID=141;_ThreadName=Thread-8;|StandardWrapperValve[Faces Servlet]: PWC1406: Servlet.service() for servlet Faces Servlet threw exception
java.lang.IllegalStateException: Context is already active
at org.jboss.weld.context.AbstractConversationContext.activate(AbstractConversationContext.java:227)
at org.jboss.weld.jsf.WeldPhaseListener.activateConversations(WeldPhaseListener.java:108)
at org.jboss.weld.jsf.WeldPhaseListener.beforePhase(WeldPhaseListener.java:85)
at com.sun.faces.lifecycle.Phase.handleBeforePhase(Phase.java:228)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:99)
at com.sun.faces.lifecycle.RestoreViewPhase.doPhase(RestoreViewPhase.java:116)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1550)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
at org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:100)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
at org.apache.catalina.core.StandardContextValve.__invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
at org.apache.catalina.core.StandardHostValve.__invoke(StandardHostValve.java:161)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
at java.lang.Thread.run(Thread.java:745)
|#]

Answer 1

Solving the concrete problem you're facing is difficult based on the limited information available, but I believe I can answer your actual stated question.
The exception you're getting is triggered when your application attempts to activate a context before deactivating the previously activated one. Based on your stacktrace it seems you are activating a new conversation before the previous one. Depending on your implementation it could simply be a timing issue but it's difficult to say for sure without reviewing the codebase.
To clarify why activating a second context is a problem, it's against the CDI spec. You can have zero or one active contexts per scope per thread, any more and you end up with ambiguity between contextual instances.
As a non-technical analogue, a scope is a shelf with boxes (contexts) on it. You can only have box open (active) at any time, otherwise your little brother (CDI container / Weld) won't know which box you meant when you said to get the action figure (contextual instance) from the open box on the top shelf (Or #Inject MyBeanInterface bean; where the bean has an assigned scope).