New network does not connect to Internet

Hi Guys,

      I have been trying to create a network that contains only one particular subnet range to allow that subnet access to External through AD/TMG groups.  Here is what i have done so far:

1. Created new network containing the required subnet range i.e. 192.168.x.x - 192.168.x.x
2. Created network rule to allow the new network (Source) to access External (Destination) with the Default IP address settings for NAT
3. Created a Web Proxy rule to allow HTTP/HTTPS traffic from the new network to External for a user group created within TMG from AD
4. Tried to access the Internet with the account assigned to the TMG group but no success

I can replace the new network with the builtin Internal network (which has the same addresses as the new network i created) and successfully access the Internet but not when the new network is in the From field.

Our system:  Win2K8 R2 + TMG 2010 SP2 w/ all windows and Microsoft updates installed.

Any ideas?  Please let me know if you require more information