W2k Pro cannot RAS with NW 4.81 client

After installing NW 4.81 client and properly configuring the laptop for RAS, a connection can be made up to 3 times then fails with error 720. Have checked and tried all knowledge bases; Novell, MS, 3COM, ect.. with no luck. Somehow the TCP\IP stack corrupts. Then ran into to another customer who said Novell admitted that the 4.81 client doesn’t work with modems. Has anyone else heard of that?