Hi herbiemmer,
You are using the same CD-key that is on the disc itself? The code on the handbook is for setting up on-line play only. Remember when entering the code to use capital letters and a '-' between each 5 code letter/numbers.
If you have done this and it still does not work uninstall GTL using the GTL disc. This will not delete any cars, tracks or personal data such as profiles, set ups. Then reinstall the game again and do not forget to also install the 1.1 update.
Cheers and good luck
Gee-Deeman
