You nav is crashing for one or more of the following reasons:

1. Badly modified OS. Restore the nav to the original BMW OS and monitor performance for a few weeks to see how it goes.

2. Weak laser, causing lots of reading errors on the disc. Fit new laser of new mechanism to cure fault.

Remember, gyro calibrates every shutdown, and nav constantly calibrates when you drive. SO a nav that may have lost calibration will need to be driven first to recalibrate.