Cannot browse LAN when connected using VPN and AT&T Air card

Our company issues AT&T Air Cards to our field guys.  They've always been able to use those cards to connect to the internet, then launch the Cisco VPN client to connect back to the office.  Then they could browse our network, get files, launch apps, etc ..  etc.  This has stopped working.  They can connect to the VPN and authenticate, but cannot go any further.  Now the wierd thing is, if they don't use the Air Card, and they can get access to a wired connection to the internet, or even a regular wireless on a home network, everything works perfect.  The problem seems to be with someting that the Air Cards use, like a certain protocol or port or something.   But nothing has changed on our network to my knowledge.   Any ideas?
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servicegroupAuthor Commented:
We were able to fix the problem, but I'm not sure why it worked.  Turns out it wasn't the AT&T cards.  It was the way we had our 2nd T1 physically plugged into the network.  I created a separate vlan to isolate the T1 circuits from each other on the DMZ side.  And now everything is good.  Our guys are able to connect to both vpn's and navigate our internal lan.
Do you have nat-traversal enabled on your vpn appliance?
servicegroupAuthor Commented:
Yes ..
Did you ever find a resolution for this?  We are having the same problem?  Are you using the AT&T communications manager or the Sierra Wireless client to connect to the 3g network?
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