Happens to me everytime.
After running MPTS and configuring settings related to IBM NetBIOS over TCP/IP, the IBMLAN.INI file is damaged.
Open the file with E and find the line beginning with net1. You may find garbage characters after net1 = TC.
A sample of the correct format is:
net1 = TCPBEUI$,1,LM10,34,70,14
Edit and save the file, reboot, and problem solved.