I too have had this issue several times on my unit. Cleaning the laser lens each time has resolved the issue for me. Ensure you unplug the unit from the mains before following these instructions.
1. Remove the outer casing,
2. Remove the 4 screws holding the PCB board at the top of the unit.
3. Remove the 6 connectors around the left/right/back edges of the PCB board
4. Now remove the PCB board
5. A metal housing plate will now be exposed. Remove the 4 screws holding this and then remove the metal plate.
6. You then have easy access to the laser lens
7. Use a cotton bud dipped in meths to clean the laser lens.
8. Now use a econd cotton bud to remove any surplus meths from the lens.
9. Re-assemble the unit (follow steps 5->2 in reverse order)
10. Plug into mains and test CD play
11. If all is well, replace the outer casing as removed in step 1.
Hope this helps. If not, I would also try dusting the internals of the CD drawer (perhaps best with an air duster)
Simon
December 2006