It's very difficult to say without seeing your application. Can you provide a stripped down example which reproduces the issue? You might want to consider bumping up to version 1.0.0.Final as 0.7 is a bit old now.
Yes I know that it is very difficult, but from Exception is not clear the reason and the point where the error occurs.
So it becomes quite impossible to create a mock in order to reproduce the error.
I'm investigating further and i'll keep you informed if i discover something else.
In mean time please let me know if you have some suggestion on how to circumscribe the error.
I have also activated the Message Trace but without success.
Thaks a lot.