I have received the same message when tried to log into the account. It was my 1st attempt within today, i didn't try 5 or more times before that, so i couldn't use up a failed login quota.
After 15 minutes i tried again and got the same result , a login attempt was failed again.
After that i used a reset password function and tried to log in with a new password. And again i got the message:
Wrong username or password. You have used up your failed login quota! Please wait 15 minutes before trying again. Don't forget that the password is case sensitive.
All these attempts have been done in Firefox.
After that i tried to log in via Opera and that attempt was succesful. Now i'm typing this text in Opera.
As a test i have repeated logins for Opera and for Firefox some times. Opera works normally, but i'm still unable to log in with Firefox , every time i'm getting a failed login message .
So i suppose that it's a technical problem on the site. It doesn't want to work properly with Firefox. Let's hope that GT's techicians will fix it soon.
P.S. Also it would be better to check this IP address 18.104.22.168
The same IP was mentioned in the email which i got from GP after failed attempt. It is not my IP for sure .
Perhaps someone is trying to hack our accounts.