Clear your browser's saved passwords (assuming you have ICS, go to Internet, click the left hand menu button, then Settings>Privacy & security and Clear Passwords at the bottom).
Then re-enter your user name and password MANUALLY. Don't copy and paste - you could easily be copying a space or similar error. Preferably turn off T9 if you can, and check that you're entering both the user name and password in the correct case, with no spaces inserted before or after.