I may have figured it out. Might want to add, to the 2.1 upgrade instructions, that people need to go to all the computers they use, and clear the cookies. I had MM2.0 list admin cookies on all of the systems I use, which was causing the same/similar problem, even though all the lists were upgraded to 2.1.

Yeah, same problem, 2.0.x cookies make 2.1.0 barf. Kinda moot to change the docs for the next release, though - 2.1.1 will have the bug fix that's in CVS now, so this'll no longer be a problem.

Bryan