This post discusses this fix. apparently punkbuster might be interfering with the rank system if you don't have it updated.
http://forums.ea.com/mboards/thread.jspa?threadID=135395&tstart=0 - http://forums.ea.com/mboards/thread.jspa?t...135395&tstart=0

EDIT

Step 1: Go to http://www.punkbuster.com/index.php?page=pbsetup.php - this website and download the link that looks like this: For Windows: pbsetup.exe

Step 2: Run the program and install Punkbuster. Then go back to the website when it is done and follow the instructions below the download link.

Basic you will want to add Battlefield 2142 to the list in the punkbuster window, then when it's there select it and press the Check for Updates bitton at the top. This will check for updates to Punkbuster BF2142 in specific, and should update something.

When it's all done go back inot battlefield 2 and hit a ranked server.. every kill you get will get you your next rank up untill all your backlogged XP is spent. Worked like a charm for me