Hi, please find above your user manual and your service manual below/
OK perhaps you may need to now upgrade the firmware or re-set up the player again using the service mode, please find all this info in these manual above. It may just be co-incidental, or perhaps your laser assembly is going faulty. Often though, it has to do with CODECs not being installed. or activated, you need to check your manuals for information.
I would wonder if the swap out, hasn't reset all your playback settings? Or the Brain, is thinking it is a differing unit now? and setting it up again may just fix your problem. Anyway please use the service and repair manual's troubleshooting procedures you should be able to isolate and hopefully repair your unit.