I'm using the software in combination with a short PL2303 based USB to Serial cable, between a Windows 11 x64 laptop and a Book8088. The driver for Sewell's own cable does not seem to install, but with this table (manually set to COM1 in device manager) it works brilliantly - it even managed to send the DOS stub over the cable. You may need to set a lower speed for your transfer - with the Book8089 I find 38,400 baud to be reliable.
I have always problems using named pipe. The handbook does not shed much light on this facility. I find it difficult to synchronize more than 2 PCs.
Windows sometime gets updated and then sometimes fastlink does not work anymore. We are mainly using W10 abd 11 Home editions.
Unfortunately, we have recently learned that FastLynx is not compatible with Windows 11. That's likely causing some problems for you. More testing is happening to confirm the compatibility with other update versions.
I used Fastlynx 3.3 in June 2021 to transfere files between a Windows 10 PC and an old DOS 3.2 PC through COM ports. It works perfect.
I'm happy to have now different version that can be either installed on Windows 10 or run under old DOS versions. Thank you for still selling this product.