Do check the information (account, password and character name) again. If it really is correct, the best course of action is to report it to support and wait a day. There has been a server maintenance just now and it has some unexpected side effects, including similar events, that are still being reported. If possible, you might want to try logging in on a different (safe) computer or reinstalling GW, this helped some people. It may be unrelated too.
I have the box ticked to save account details and char name so it's only the password that needs inputting, and as it's the same password I use for a couple of things I won't happen to forget it / spell it wrong......