Why can I apply to either Cambridge or Oxford but not both?

I am a student in America and I would like to apply to both those schools in England. For Oxford, I chose a course in Physics and for Cambridge I chose "Education with Physical Sciences." However I got an error message: You have chosen a course at the University of Oxford and the University of Cambridge. This is possible only if you already have a suitable degree or will have been awarded a suitable degree by 30 September 2014, and you are applying for A101 (graduate medicine) at both universities (and optionally also A100 medicine at Cambridge). So I can only apply to both if I apply for medicine? What? How can I get past this? Thank you.