lost packets ? NT4.0SP6 net problems

LAN with NT4.0 SP6 SBS SBO server, less than 20 clients on 10 MHz ethernet TCP/IP.
Have problems with a CAD that uses up to 100 files and swaps up to 20 Mb/update. It corrupts the data base repetitively on updating (missing EOF). This DOES NOT happen copying the structure locally. No error message at all on server or workstation. Will upgrade to 100MHz, but what can be the cause and how could I trace it to feel that situation is under control ? (it is not a problem of simultaneous write accessto the DB)
THANKS. Mike