ERP Course selection glitching out really bad.

Im trying to select my Depth/Breadth elective (along with other Depth electives). Every time I try to finish my registration, I get the prompt: "The subject XXXX is not available. Please apple for another subject." This only happens for the Depth/Breadth elective. What do I do? I changed the subject in that Depth/Breadth elective, but the same prompt remains, only the subject changes. Im at my wits end. Spent an hour on this BS.