Same problem here. Trying to change user forum permissions to put user on approval for all forums.
Have done it many times before, now getting a "the submitted form is invalid" error.
Did manage to put the user on approval for one forum only.
We have a lot of forums, I don't want to have to do this one forum at a time, every time someone needs to be put on approval.
I do not think it is related to an upgrade because I put 2 members on approval Feb 1, 2014 and we have not upgraded since then.
We did move to a different host.