It can fail in the activation attempt due to an invalid license key and connectivity issues. However, it can also occur if the licence key exceeds the activation limit.

Dead Space 2 became available for pre-purchase on digital download service Steam yesterday. It went live early this morning. So why aren't Steam users able to play it yet?

With the PC locked up, and the valid Windows product key being labeled as invalid, the average user would likely call the tech support number on the lock screen.