I have the same problem with writing to a Yaesu FT-60 handheld.  I can download from the FT-60, but when I write I get a "Failed to communicate with radio: Radio is not responding" error.

I have checked the issues page and see there was a issue with writing to the FT-60 that was deemed closed after reloading drivers for the Prolific Chipset.  My USB/RS-323 interface is a FTDI.  The interface is a homebrew RS-232 to TTL level shifter that works, with a different cable, just fine to read and write to my FT-8900R. 

I suspect there is some timing differences between the two radios.

The computer is a Winders 7 - 64 bit 3gHz I3 Processor with 8 gB ram.  I am running the latest download of Chrip (4/19/16).

Is there any logging going on in Chrip that I can enable and look at?

Regards,

Bob - N4RFC