According to Eurogamer, a Windows digital certificate has been the cause of many problems for many Gears of War players on the PC recently. Many players have been unable to start the game due to a hard-coded date in the certificate that prevents the game being played from that date onwards.
Players have received a message saying "You cannot run the game with modified executable code. Please reinstall the game". The issue has brought up more questions in regards to the role of DRM protection methods, with many wondering if Gears of War is alone on this issue. TorrentFreak has reported that pirated copies of the game have also been affected by the issue, saying "it must be well hidden if the usually alert crackers didn't spot it," and raising concern about whether any other titles will be affected by similar issues.
A super-moderator on the Epic forums has announced that the issue is being worked on. In the meantime, several temporary fixes have been found. One of these includes setting the system date back to before January 28 2009, but of course that may present issues with other things.
There's been no comment from Microsoft, the publisher of the game, as of yet, but Epic are working with them to resolve the issue. Nothing has been said about whether there will be the same issue with other Games for Windows titles either, although it's likely that this is just a one off slip up, only affecting Gears of War.