This sounds like a connectivity issue, possibly related to the USB-to-serial device you're using or the baud rate set. Unfortunately without having the device present here to test with, those are the only things I can think of to check.

When we added support for the IIIc we had a device present to test with, and so far everyone using those devices has had success with the SkyDemon interface, so this case is troubling.

I have a Skymap IIIC which I connect to my notebook using a serial to USB adaptor (it appears as COM 6). I can download logs using Navbox Proplan 5, but if I try using Skydemon 1.3.2 I get an 'authentication error'. If I try to upload a route, it connects and appears to work, but only about the first half of the route is loaded.