Years and years ago, Sony went on a war against piraters by developing a new copy-protection scheme on CDs that would supposedly prevent it from being duplicated. Unfortunately, their method resulted in massive outcry from the community, as people learned that new CDs they'd just spent $30 on wouldn't play in any computer and often wouldn't work in many standalone players either! A relatively new DVD protection scheme from a company called “ProtectDisc” is already creating similar outcry, with rumors of discs created with it being unusable in a Windows PC:

So if you pop in a DVD "infected" with Protect DVD-Video, it can't be read by Windows Media Player, Media Center Edition, or any DirectShow-based software, thanks to a Universal Disc Format that tricks your machine into believing that the IFO file is zero bytes long.
Of course, that would immediately be disaster for any company foolish enough to push DVDs with that form of lockdown. The number of people using PCs as media centers is more than ever, and grows every day. Companies like Intel and AMD are pushing for the PC to be the focal point of home media. Imagine how happy someone will be after they purchase a brand new Viiv branded machine and find that a bunch of their DVDs simply do not work with it.

There are 3rd-party workarounds already, though relying on a 3rd party isn't an acceptable solution to some. Rather, this is probably a ploy to get someone to install a player that ProtectDisc wants you to install. DRM continues to aggravate legitimate users far more than would-be pirates, and ProtectDisc doesn't look like it will make things any better.