Hi Terry,
I have the same system [for about 4years] 2 years ago the same fault was happening with my satnav. Panasonic tech department told me that the disc was probably scratched or faulty, I bought a new disc from navteq[150 quid] but the fault was still there, sent the unit and new disc to panasonic. After waiting for about 4 weeks they sent it back too me fully refurbished stating that the laser reader had failed,although out of warranty they did not charge me .
hope that this info helps
kevin wright, December 2007