Mark,
I run Flrig 1.3.51.02 (alpha testing it), and have run all previous versions, with my FT817nd with no problems.? Early on when I first got my FT817nd, I found it "worked" at high baud rates, but was prone to CAT errors.? At 9600 baud, it's rock solid, so that's where I run it.? Set the radio CAT RATE menu (#14) to 9600, then set Flrig to 9600 and try that.
Here is a screen shot of the settings I use on my Linux Mint system:
My serial port is a USB/Serial adapter with a home-brew cable for the CAT interface.
73,
-Joe-
K0OG
Joseph Counsil