Player is increasingly unable to read new dvds. Cause?

Sometimes it is due to a dirty read lens in the unit. More often it is due to newer DVDs having newer security encryption algorithms that the older units are not compatible with. You may want to check to see if there are any firmware upgrades for your unit that may bring it more up to date on the current encryption standards.

The main cause is that new DVDs are usually formed with newer formats. For example, if you play a DVD with a CD player, then none of your DVDs will be readout. The worst case could cause damages to both DVDs and disc players
You can check on this tutorial for such kind of solution:
My Old DVD Player Won't Play New DVDs? Solved