I've the same problem since I updated to Thunderbird 5.
I tried everything but i haven't been able to make it working.
I tried installing Enigmail 1.2 from their site, removing the old in "/usr/lib64/thunderbird/extensions/".
But nothing. Then i waited the 1.2.1 version, but nothing again.
I don't know what to do now.
I think gpg works correctly, since KMail works with it.