The ft 891 com port drivers must be installed before the setup exe is run.
check for the proper baud rate and that Cat control is ENABLED on the rig.
I know you read and followed the README file, so did I, but the driver install failed on my first try and it didn't give me any message about the failed install.
After I installed the drivers (the second time), I rebooted the puter to ensure they were loaded. then I ran the actual program setup
I had to COMPLETELY remove the installed extracted program and the downloaded ZIP files....... and then re download it after my first install attempt failed, then it installed properly from the setup.exe file.