I'm not sure why you are "talking" to the printer this way (using the FOPEN() function), however, if this is how you need to communicate with the printer, the problem may be with you "calling" LPT1.DOS instead of PRN. If I am correct (and I'm just guessing) LPT1.DOS is not a direct call to the printer port - it only "represents" the port to the OS. Check it out...
Good luck,
Bill