Optiplex GX270 unable to join domain over VPN

I purchased 10 new GX270s with the intention of joining them to my domain over VPN via a Cisco 1711 router.  The tunnel is always active in the router.

None of the 270s will join the domain.  I receive one of two errors after it asks for a username and password of a person authorized to join the domain.

"The semaphore timeout period has expired"

"The domain CBHS is currently unavailable"

We currently have a Dell Latitude D600 at this location and it joins the domain without a hitch over the same connection.

Two of the 270s are using wireless cards and the other 8 are using the built in Intel gigabit ethernet cards.  Whether I use the NIC or the Wireless card they still timeout and will not join.

Things I have tried to reolve the issue.

Obtained latest drivers for the NIC and Chipset.

Disabled the onboard NIC in the BIOS and used a 3rd party NIC.

Updated the BIOS to revision A04

Compared all services running on the D600 and matched them with running services on the 270s.

Confirmed all TCP/IP settings match between the D600 and the 270s.

Has anyone else experienced odd behavior with the GX270 and any network related issues?  I experienced some odd behavior with some GX270s and Powerquest Drive Image about 6 months ago.  The NIC would intermitantly not initialize with the Drive Image Boot Disks.

ANY information would be GREATLY appreciated.