Why is my usename wrong?

Why is my usename wrong? My other usename is shenglong and I don't forgotten password.
The system prompt '' You have entered an invalid username or password. Please press the back button, enter the correct details and try again. Don't forget that the password is case sensitive. Forgotten your password? Click here! You have used 3 out of 5 login attempts. After all 5 have been used, you will be unable to login for 15 minutes.''
Could you give me a hand?

When did you register? There was a database wipe (unintentional) recently so that probably lost your account.

I register on April 18, 2013 .

that explains it.