There are several bugs in the pack implementation in Zope 2.6.1, some of which could cause data loss. I fixex these bugs a couple of weeks ago, and sent a status report to the zodb-dev mailing list. I should have reported the resolution more widely, because the possibility for data loss is of interest to wider audience than reads the developer list. The technical summary I posted on zodb-dev is here: http://mail.zope.org/pipermail/zodb-dev/2003-May/004945.html The long and short of it is that we have a better test suite that provoked the known bugs in 2.6.1 pack. And we have a new pack implementation that fixes all those bugs. I had originally planned to leave Zope 2.6.x as it is, because the changes involved in the new pack are fairly significant and we only had one or two isolated reports of problems. Since several more people have reported problems, we've decided to add the new pack implementation to the Zope 2.6 release branch. We need people to test this code! If you have had problems with pack recently, it would be really helpful if you could run the new code on your database and verify that it fixes your specific problem. Jeremy