[nsp] IOS Tunnel Problem (or is it?)

[Drix Tabligan]

Hi,

I've been stumped for a few days already. Here's the scenario.

Router A is directly connected to Router B via E1 v.35 interfaces (link
C).
Router A is connected to Internet at point A v.35
Router B is also connected to Internet at point B v.35
Router A has equipments connected to Fast Ethernet port which includes
   Lucent TNT, 2 Win2000 servers.

A tunnel is created between Routers A and B via their respective
internet connection points. Each is using it's own serial interface ip
(upstream internet provider) as source with the other router's serial
interface ip as the destination for the tunnel interfaces. Eigrp is
running between both routers on both serial interfaces as is iBGP to
aggregate the routes. When link C is up traffic is ok and eigrp prefers
link C due to its lower cost. All equipments connected to Router A via
its fast Ethernet are reachable. When link C goes down, the tunnel
interface should reroute via the Tunnel interface which it does fine, as
eigrp should do. Problem is, I cannot ping the Win2000 servers on the
Fast Ethernet segment in Router A from Router B, even though I can ping
the Lucent on the same segment. When link C goes back up, the problem
goes away.

What gives here? 

Thanks in advance for your ideas!

Drix