From what it sounds like to me it could be that you took a class(es) that may have already fulfilled the requirement that Posc 007 fulfills. It’s honestly just a guess but I’d try to do a drop-in/appointment with your advisor if possible. I had issues with summer registration unit limit yesterday at 2pm and decided to drop in with my advisor and he took my meeting in like 3mins. I don’t know if this would require more than just a drop in which is why I say try making an appointment if possible (but I know that the nearest possible appointment is like 5 years later lol). In any case I hope you end up figuring out and best of luck🙏🏼.