Remove the barrel and work the barrel release, make sure the latch(barrel catch) is moving its full range, it may just need a good cleaning internally. See the Trigger work links in the Centerfire FAQ and Help sticky to learn how to R&R the trigger and latch. The barrel fitting links may also help in determining what's wrong. When it's locked up properly, the barrel release should be loose, if it's not, there's a problem.
Tim