I’ve seen the thread pool error a lot but inside an Orchestration.
I don’t believe it’s any type of bug – it’s just .net running out of threads.
There are some KB’s that talk about how to add some threads or make changes. I never really got things to work well under load through. I usually died around 20 connections.
This might help: http://groups.msn.com/BizTalkRocks/general.msnw?action=get_message&mview=0&ID_Message=96
Otherwise, I know there are some KB’s on it.