I bought The Evil Within, including Fighting Chance pack ( PC - New + Unused ) as a gift for my son for Christmas. When he opened it, and tried to install it, he continually receives the message "This CD Key is already in use by another Steam account."

He is using the correct game key, printed on the back of the control manual, and not the key for the fighting chance pack.

Some help with a working CD key would be good thanks, if anyone could oblige. It's pretty poor when someone can't even install their Christmas present.