I am not familiar with that software. I do not know if your cable is correct, nor if your communication parameters are set right. I do not know the length of the file, if the file is written correctly, or if it has the correct extension. Is it a G & M code file or a convesational file? What created it? As you can see there are a lot of places where the file transfer can get into trouble.
Why are you using the RS232 when the floppy drive is available?