Accept non conflicts and save test plan results in an error message

In RQM 6.0.1 , we tried to see how the merge conflict works when the same test plan is modified by 2 users, so 2 users added 2 test cases to the same test plan simultaneously , once the first user that made the change tried to save ,the conflict message appeared (since the other users already saved his changes) and the user had to hit on the accept non conflicts changes , but when trying to save the test plan an error message ' Unable to save test plan, an internal error has occurred, see server logs' displayed.

is this an expected behavior? what could have caused this problem?.

Thanks In advanced,

Lior