unable to connect to win2003 domain controller

here's what's happening...have a network with 3 offices
all in different towns connected by a cisco Pix vpn. the
main office with the server is here and the users here
can log on just fine. in one of the branch offices they
can log on just fine also, but in the other branch office
when a regular user tries to log on it says unable to
find domain controller. if i try to log on using the
admin account it logs on, but if i start browsing the
network and click on the server to get to a user's folder
(used to store documents and stuff) it pops up with a
login screen with 2 heads...similar to messenger. if i
try the admin account there, it won't work. if i try any
other user's account it works just fine and i'm in. any
ideas? i've never seen this before and doesn't make
sense. the server is obviously just fine otherwise the
other 2 offices wouldn't work right. i've tried blowing
away and recreating the accounts for that office thinking
maybe somehow the rights got messed up or something...

thanks for any help!!


erik