Stephen,

I've been fortunate enough to not have to do an upgrade on an exisitng project to 6.0 but here's a thought or 2 to check maybe...

mmDataEnv.dbf still exist? is it readonly by chance? I get the same error when VSS has that sucker ReadOnly. If it's there and writeable, then check the values in mClassLoc fields to make sure they all be a pointing to a place that exists. HTH & Good Luck!