Remote IBM3151's drop echo until reboot

[RonnyDonny]

We are using IBM3151 terminals at a remote site using a VPN connection, Cisco 1600 and Etherlite server. If the connection is interrupted, we lose echo from the RISC to the terminals. The terminals receive from the RISC but can't send to it(they get the logon prompt but can't logon). The only way we have found to fix the problem is to reboot the RISC. Is there some other way around this? We've power cycled the router, the etherlite server as well as the terminals themselves. I also tried going through change on the els in SMIT and that didn't work either.

Any help would be most appreciated.
Thanks,
Don Ross