@David
I have upgraded eZ from 3.6->3.8 and 3.7->3.8 few times and I had a problem this once.
What I did:
I used two machines: I installed eZ (with my ini configuration) on one computer (XP system), and used database on another cpu (with Linux system). And it worked, but I dont know why. (when one machine with eZ and database together: bad success)