Hi,
Some informations:
Session beans do not support concurrent access.
EJB by default prohibits concurrent access to bean instances, if for example one of the clients invokes a method on the EJB Object, no other client can access that bean instance until the method invocation is complete, if the method is part of a larger transaction the bean instance cannot be accessec at all, except within the same transactional context, until the entire transaction is complete.
regards.