Win2K Dialup Err -Could not agree on PPP

When dialing in from remote locations, users get dial tone, dials out, shiva connections, but when authenticating, receive error 720 “Connection failed due to PPP” “Could not agree on PPP Protocol”. Network connections are fine, and seems to work fine when dialing in from home, but not while at Hotels/Motels? We are running authentication from a Shiva device and our Domain is NT4.0… Please help!!!