if you're running within an application server, you shouldn't be creating your own threads. the AS performs thread management for you.
your exception is probably because you've started a new thread but haven't properly associated a session with it.
hmmm...i am surprised to knw that I am not supposed to create my own threads within the AS...
My situation is that I have to perform some job over the ntw and it cannot be done serially, i need multi threading to speed up the job.