It can be due to either...
1. Faulty disc, (first ensure there are no fingerprints or scratches on reflective side).
2. Faulty drive.
3. Faulty digital process pcb.
PS. To remove a stuck disc if unable to with recovery displayed...
Place the unit into standby by pressing the [Power] button for 10 seconds. Then simultaneously press [Stop] & [CH Up] for 5 seconds.
Otherwise you need to return the unit to Panasonic for service.
Cobweb
January 2005