Do you have any special characters in your login name or password (such as a letter with an accent mark - é, á, ï, ß, etc)? If yes, you need to Email M&A to have this corrected. The game cannot use special characters. Alternatively, some players have stated that you can copy and paste the affected character from another place (such as a Microsoft Word document) into the password bar.
The password is case sensitive when you log into the game client, but not to the forums, as well.

Odd... Do you still have the confirmation E-mail for the account? It should have the password you registered with. Try copy/pasting it from there if you can.

And on that note, was the account ever confirmed? It'll give you a password error in the game client if you haven't, but you can log into the community without issues usually.

Sure thing, glad you got it fixed!