Serial port and VC++

i made a software in VC++ (compiled it on win 95)
it accesses the serial port(through standard "ReadFile & WriteFile" commands)
and transmits data onto some hardware connected to the PC, through the serial port. when i tried to run the executable on win NT, it said that it can't access the port.
i even tried to run the executable from the administrator's account, just to make sure that you don't need administrative priveliges to access the port.
but it failed even there.
how do i fix this problem?

thanks in advance.

maybe, you just solved the problem, but here's one possible reason:

Even if you don't use XON/XOFF protocol, you have to setup reasonable buffer lengths for XON/XOFF under NT, under '95 you don`t have any problems.