I just found a solution and joined so I could post it.
I tried everything possible suggested in dozens and dozens of threads with the same problem. I reloaded DX, rolled back to wmp10, played with accelerator settings, reinstalled video drivers, added , deleted and promoted various mpeg2 decoders etc...
but finally a light went on!
Maybe this is a audio problem and not video at all.
I went into wmp under tools/option/DVD/Advance and found an Elecard Mpeg2 decoder but I was sure that I had originally installed an ac3 filter for audio. I searched my system for the Elecard decoder and found an entry in the "programs" directory. I just renamed the whole Elecard directory to Bak_Elecard and rechecked the wmp and this time it showed the AC3 filter. I tried a couple of commercial DVD's and they both worked!!!
In case you need the AC3 filter the one that works for me is 1.45b. I tried others but had no audio. I'm not sure about posting links on the site if it's not permissible then please remove it with my apologies. The version they have currently is 1.46 but I haven't tried it. ac3fillter
I'm pretty sure that once the wrong audio codec is removed the video will play even without the ac3 decoder but you probably won't get audio.
At least that idiotic misleading message is gone!!!!!
btw) You may have a different audio codec showing than mine (Elecard). The idea is that it can't decode the audio so gives a cryptic message about copy protection.
Edited by tundraman, 25 January 2008 - 06:41 PM.