AA, in my experience, is always suffering from some kind of problem at any given time. But it's probably because Punkbuster is out of date: go to evenbalance.com
and look for the AA Punkbuster update. That is very probably the solution.
If this doesn't fix it, try the AA forums at forum.americasarmy.com
. People there can help you.
Well done on downloading AA, it's good fun!