I have spent about 30 hours total on the phone with Linksys and with AT&T trying to figure this out and I am sure that someone has run accross it before.
I have an office in Cleveland that has a 2wire DSL modem/router (AT&T DSL) in bridge mode with a Linksys RV042 and all is perfect. The PPPoE works perfectly and the Linksys gathers the static IP without issue. I have set up VPN clients and as of now no one using an AT&T DSL connection can connect (using Quick VPN) and anyone using other ISP's have connected fine.
I have an office in Dallas that has the same 2wire devise and the same RV042 and the ONLY thing that works is I can connect to the internet with the 2wire in router mode. When I switch it to Bridge mode I cannot connect (remember Cleveland connects perfectly) therefore I can not create the VPN tunnel, and no one can connect using either QuickVPN or a Cisco VPN Client. I have tried to put the 2wire in bridge mode and use a brand new router (The non VPN Linksys one I forgot the model) and the results were the same.
With Dallas on the internet using the 2wire in Router mode, I opened every port to try using the VPN client to no avail.