Paul Are you running FSSession0.4.0? If not please upgrade. The problems you mention below have been corrected. Nevertheless the first problem you descripe is not really related to FSSession. What happens is that certain Zope objects that can be pickled should not be stored in FSSession. Initially FSSession used marshal to serialize python objects, which is faster and does not allow storing of instances etc. I moved to pickle at the users request but one should be careful what he/she stores in FSSession. FSsession-0.4.0 should not raise an exception in tpc_finish. If I understand Zope's two phase commit mechanism, it is ok to raise an exception in tpc_begin (which corresponds to the 'polling' stage i believe) but not in tpc_finish. So now potential problems like full filesystem, unpicklable instances etc should be caught in tpc_begin. Pavlos