* GENERAL: Wrong type of serial cable. A specific type of cable is required.
* VINTAGE PC: Cable attached to the serial port of COM2, but you incorrectly believe that it is COM1.
* VINTAGE PC: Cable attached to the serial port of COM1, but you incorrectly believe that it is COM2.
* VINTAGE PC: The serial port you are using is faulty. Fully check it (including external loopback test) - see the 'Testing a serial port in DOS' section of here.
* VINTAGE PC: You did not type the MODE and CTTY commands properly.
* VINTAGE PC: Verify that your first serial port is configured for: I/O port of 3F8, interrupt of IRQ 4
* VINTAGE PC: Verify that your second serial port (if it exists) is configured for: I/O port of 2F8, interrupt of IRQ 3
* MODERN PC: The serial port that you are using is faulty. Test it using appropriate software.
* MODERN PC: Your serial port is a USB-to-serial adapter, not a serial port built into the motherboard.
Just a possibility.
On my modern PC, the serial port built into the motherboard works flawlessly with FastLynx.
But of two different make-models of USB-to-serial adapters that I have, only one works to transfer the 'bootstrap slave' - see here.