I don't understand. I just bought the game and it has an invalid CD KEY? this is unacceptable!

So I got a response with a key...ran the reg file, checked my regedit and saw that the key was updated....ran UT2k4 and then low and behold, CD Key is banned.

Does GOG not give out a unique CD Key or are all these keys recycled?

How do I get a refund?, this is ridiculous.

Contact GOG support (again?), either ask for a new cd key or for a refund.
More info onn GOG's refund policy: http://www.gog.com/support/website_help/money_back_guarantee

I recently had that issue. GOG fixed it via sending me a .REG file.

The problem arose when I got the Steam version of UT2004 (gifted to me). It had probably over-written the original .REG file. That's when the GOG version began acting up. Since then, I've uninstalled the Steam version, but the GOG version kept giving me the "invalid CD key" message and not launching. The .REG file GOG sent me seems fixed the problem. So GOG users need to be wary of the .REG over-write that the Steam version causes. They did that for me this morning. Works beautifully.