Apparently Hibernate does not support fetching two Bags Eagerly at the same time.
See problem here http://forum.hibernate.org/viewtopic.php?p=2310316&
I found a solution to the problem, described here in two blog entries
http://jroller.com/eyallupu/entry/hibernate_exception_simultaneously_fetch_multiple
http://jroller.com/eyallupu/entry/solving_simultaneously_fetch_multiple_bags