RADIUS Cannot Authenticate

We have 2 buildings with 2 cisco routers. Each has NM-16AM modules for dialup users. These 2 buildings are interconnected via a lease line. We have only one RADIUS Server (Cistron Radius 1.6.4), which is located in one of the 2 buildings. When I dial to the building where the Radius Server is located I would be authenticated, but when I dial to the other building i don’t get authenticated.
Need Help.

thanks,