Here's an aritcle on it:
Sony warns of major glitch in Holiday 2004 Demo Disc
SCEA alerts public that playing the Viewtiful Joe 2 demo will erase memory cards.
Over the past few weeks, members of the PlayStation Underground--Sony's US fan club--have been receiving copies of the Holiday 2004 Demo Disc. One of the premier demos on the disc was for Viewtiful Joe 2, which arrives on the console December 7.
Unfortunately, gamers eager to sample the cel-shaded beat-'em-up were in for a very nasty surprise. That's because the demo contained a glitch that will erase all saved games on the memory card or cards currently inserted in the console. Considering many PlayStation 2 owners are currently shooting their way through Grand Theft Auto: San Andreas, which takes at least 40 hours to finish, the glitch sparked an uproar among PlayStation Underground members.
This week, Sony acknowledged the glitch via a mass e-mail to PlayStation Underground members. Besides conveying the corporation's "sincerest apologies for any inconvenience this may have caused," the e-mail also suggested that gamers "please remove your Memory Card(s) from your PlayStation 2 computer entertainment system before you load the Holiday 2004 Demo Disc." Speaking to GameSpot, a Sony rep clarified the situation further, saying, "You can play all of the demos including VJ2 as long as you remove the mem cards."
By Tor Thorsen, GameSpot