You should take this situation up with the chair or your department or the dean. I'm sure that there is an appeal process. If you go to a medium or large school, sometimes there is some rule or situation that you don't know about and their first reaction is to go by the book. If you can appeal and show them that you deserve to do your student teaching, they may approve it. It couldn't hurt.
Also keep in mind that they have a certain standard to uphold, especially with teachers to ensure the degree they are granting you states they endorse you as a teacher. If there is a rule that states you have to have a B or above, its only ensuring the quality of their alumni. When you have kids in school and you put their education in the hands of their teachers, it's reassuring to know they take the right measures to ensure the quality of the teacher's education.


