This is not a mistake, there is a reason why this has happened and do not worry this can be fixed, but it will involve some more work from your end. The way that GoG.com works is that there is no DRM or cd-keys, etc. All users who buy UT2004 on there get the game with the exact same CD-Key.

As can you can guess from a ban enforcement standpoint this is a problem. This CD-Key is used highly in the warez scene too because there is no DRM. If you legally purchased the game, please contact their support from the email that you used to purchase the game. They will verify your purchase and get you a custom cd-key in 1-2 business days.

We apologize for this inconvenience, but it is not our fault. It's GoG.com