If you have the FAPT option on this control, then when read the program into the Fanuc 3T, it will either read from the FAPT board or from the external serial port. Look for a button that switches back & forth between the "NC" and "FAPT". Make sure that you're in "NC" mode.
If that's not it, look at parameter 005, bit #2 (the 3rd bit from the right). It should be a "0" for RS232.