Windows Media Player cannot play this DVD because there is a problem with digital copy protection between your DVD drive, decoder, and video card. Try installing an updated driver for your video card.

For those wanting to jump on the Blame microsoft wagon, i just wanted to tell you this:

        I got that error tonight. on a dvd drive i always use. I looked to this after trying the video driver update and it not working. But put the disc straight from the dvd drive to the dvd burner i usually only use for burning and the disc started no problems. I'd say it's a hardware or driver issue with the drive not WMP. not that i always love microsoft we have our fights, and IE is a joke but nothing is perfect.

This is another example of Digital Rights Management (DRM) and similar anti-piracy tactics hurting paying customers. I recently reinstalled Windows on an 8 year old Gateway and just ran into this problem with Windows Media Player. VLC also doesn't want to play my store-bought DVDs. I remembered that I originally had to purchase WinDVD so that I could watch movies; it contained the necessary codec. Unfortunately, when I tried to reactivate WinDVD, I ran into a series of brick walls. Another

Then I remembered that a later purchase of Roxio Easy Media Creator 8.0 also contained a DVD codec. I'd already reinstalled Roxio and fired up its DVD player. Lo and behold I was able to play DVD's on it. But I still can't play them on Windows Media Player or VLC.

I don't know what exactly caused these problems, but it seems to be related to more DRM madness. I recognize the need for these companies to protect their intellectual property, but it so often seems that the last people whose needs are taken into account are legitimate customers.

JohnD support operators suggestion works great. The trick is to find the correct driver to uninstall. Click the START button in search for program type update device drivers. Go to dvd/cd-rom drivers then go to your dvd device which for me is HL-DT-ST-DVD+-rw GA31n ATA device uninstall it restart your computer then reinstall the device driver for your device and that should fix any corrupt data for the copy write protection.

This was a gigantic annoyance for me and similar to everyone here this appears to be some kind of DRM issue.  I tried all the suggestions mentioned above, re-installing the latest drivers, upgrading to WMP11, installed the latest K-Lite codecs and the XP codes (since my machine is XP).  I even tried the Windows Media Player Classic that comes with these installs to no avail.  I have definitely played DVDs on this machine before and now nothing will work.  I downloaded a copy of VLC Media Player and the good news is that it actually displayed the menu of the DVDs (which I presume are not copy protected) but was not able to play anything else.

This is so annoying to have purchased a laptop and a DVD but not be able to use it, maybe if these movies production companies didn't pay $50 Million to people who's only skills involved looking attractive and being able to read someone's else lines we could watch these movies.

Anyway, hope someone else has better luck out there.