We have 10 users using contribute 3.1 on a domain to make
changes to their departments portrion of the website. I have one
user suddenly getting access denied errors to pages she was
previously able to edit.
We had that happen to a user whose permissions were all
correct. Turned out her Active Directory entry had changed and the
AD settings in the CPS had to be updated to include a new group (or
something like that--I don't handle that part, so I'm afraid that's
all I know).