You should be able to enter it with 0 credits and no grade. I'm a reapplicant and my classes in AMCAS rolled over from last year. When they verified my transcripts, they put in AP CREDIT as a "class" with no grade, just credits. So I get a red text message that you have a class without a grade, and it says that this may or may not be acceptable. I'm leaving the "AP CREDIT" with no grade and figuring its an acceptable case. Sounds like it's acceptable in your case too. When they verify your transcripts, this will match up and I don't see why it would be a problem. Good luck!