Why is my user name or password not accepted?

There could be a few different reasons:
A) If you are a new advertiser and your user name is not accepted it just means that it has already been used by a previous advertiser. In that case, just create a new one.
B) Make sure there's no spaces between characters.
C) Your new user name or password could be too long.
D) Always remember that the user name/password is case sensitive.