Log into your Gmail account to verify that you have the exact user name and password, and have the correct upper/lower case letters. Try it again on the phone.
If that doesn't work, you are going to have to do a factory reset on the phone.
Turn it off, hold the "X" key on the keyboard and turn the phone back ok. Keep holding the X until it comes up to a screen with an exclamation point. Press the down volume key to take you to a menu. You can then select (with the D-pad on the keyboard) the reset to factory option, reboot the phone, and follow the prompts.
Another option it to try to use the Security exploit that has been discovered in Android 2.0.1...
“It has been observed that on other Android phones, if you try to access any applications or data, while the incoming call is in progress, you will be asked for the unlock pattern. However, on the Droid, if you select the “Back” icon during the call you are taken to the “Home” screen without being asked for the unlock pattern. Once you are at the Droid’s “Home” screen, you have full access to all applications and data; for as long as the incoming call is in progress, and you do not select the “Home” icon. When the call ends, or you select the “Home” icon, the Droid asks you to enter the unlock pattern,” a recent article on theassurer states.
Basically call your phone from another phone, you should be able to answer it without the unlock code... Then hit your "back button" while in the call which should take you to your home screen, go to settings, security, and try removing your unlock code. I don't know if that will work or not, but it's worth a shot. 
