Could you let me know which version are you using? Also, if you're able to reproduce it 100%, please start it from terminal (run-standalone.sh python2.5 /opt/mfefolders/mfefolders.py) so if you get an error it will remain displayed. I don't have access to an MS Exchange server atm, so there could be some cases (lots of folders, complex subfolder structure, etc) which I didn't test yet.