I have both Call of duty and the united offensive expansion pack. I installed Call of duty. Eben though i got an error message for not detecting the DISC 2, i managed to copy the *.pak files from the cd to hard disk where call of duty files have been stored. Then the game worked. But when i started installing the expansion pack, it gave an error message saying that there is no valid installation of call of duty in the machine.
What could be the problem? please help me.