My rank is stuck.

Hello everyone. I just got the free version of Halo Reach and while playing I noticed my rank wont move. Here’s whats going on. No matter how many cr I gain my rank wont go up. It does show the bar moving, but it simply restarts from where it was before and never going any higher.
Any idea on how to fix this problem. It really sucks, because I forgot this was happening before and why I stopped playing.