From the manual:
"Game failures
This type of error refers to an error in the Project64 application or plugin(s) that is handled succesfuly by the application or plugin error handlers. a good example of this is the "UnHandled OpCode" error (OK, the OpCode itself is unhandled, but the situation is handled - you can end emulation, reboot the game, or play another game, without Project64 crashing). Another example is a graphics Access Violation. This type of error neary always indicates a bug or a configuration error in the emulator.
Are you running a supported game with the correct ROM settings? Almost any game will crash without the correct configuration.
Anything you can do to improve core security (ROM Settings) may prevent the problem."
Make sure you are using the most current Rom Data Base file from the main page, and make sure you are using the default plugins. Also make sure that your system meets the minimal requirements according to the manual.