This is up to you to figure out or get help with from your provider.

What you need to do is insure that all of the router requirements that are listed in the setup instructions (and in my Tech Guide, link in my sig) are met.

Once you took the router out of bridge mode, certain defaults were set in place which prohibits the MicroCell from establishing a secure, 24x7 VPN to the AT&T Mobility Servers. and all of the 'router configurations' that are required for the MicroCell to work were met. In bridge mode, the router/modem was just passing data thru without any filtering, etc. Unfortunately there's rarely an easy fix for router issues.