There is no default password. Somehow one was set. You need to move the battery jumper from internal to external if you have the NI-Cad type CMOS battery. This will kill all the CMOS settings and the password.
If it is a newer MB such as the type with a "coin"style battery, remove the battery and wait a while and see if it is cleared.
But I wonder if the battery is low. Why else would you be getting a CMOS mis-match error?