Just an update on this, I am having the same issue. I have tried all the fixes (logging out, time fix, deleting .dll's, etc) and can still only randomly connect.

I can connect to almost any other server besides n/u servers but I get the error no matter what n/u server I try to join.

Additionally, I have had some of our GG regs tell me that they are having the same problem and that the fixes were not working for them and that they had to mplay other servers because of it. (and it's working fine on other servers for them as well)