Program that works on 10 diferent Win95/win98 machines and uses serial communication thru COMM port doesn't work on Windows NT Workstation / Server

Please, send me some tips how to programm COMM the right way. I modyfied my code on and on and tested in NT but with no success.

Please help before I buy new disk and install NT Workstation on it and run VB on it.

How my program works:

open comm port ...OK
send data to port ...OK
wait for 1s
on comm event
read data ... no data recieved

Thanks