Oh you said *one of* the originals doesn't work. I'm guessing you made a slight error in your reprogramming. Try it again. You skipped something during the programming of the 3rd or 4th key as you need the first 2 to program any more.
There is a parameter in the PATS system that limits how many keys can be programmed. Try to program them again, but if it still only holds 3, you may have to take it to the dealer to have them access the PATS system and make sure it's set up to allow more keys.