Hi...
This is the problem we faced. This happened when we are using MVC architecure for our portal.
What happened is when submitted twice requests are sent to same controller and controller is not
thread safe.. So shared objects like session objects, Application objects are corrupted and when these corrupoted objects (Usually value beans stored in session/Application)are used in
JSP code this exception is thrown..
We resolved this problem by disabling submit button after submission..
One more solution is making
servlet and other related components thread safe by implementing SingleThreadModel but this may pose a serious performance problems.
Hope this helps..
Rgds
Manohar