Can someone please tell me what im supposed to be doin??

Ive completely alot of the trainin, medic, marksmanship, airborne, even the first part of special forces.

I go onto deployment, missions, i select the first infantry trainin MOUT one, and everytime i select a server to join even the official military ones, it connects me, then i choose a team then i get kicked back out to the main screen again??

Why??

Any erm beginner guide for me here would be helpful, cheers.