Solved Repetier Host v1.6.0 crashing - "communication timeout" in logs

so I recently upgraded RH to the latest version - mainly because I was tired of the pop-up bugging me that there was a newer version available..

anyway, things worked pretty well for a while (a couple of weeks), the latest version of Slic3r bundled with it is nice too - has some new features that I am liking.

Now, for no apparent reason, it has started "crashing" - RH stops responding to commands & printer stops dead in the middle of a print.

at first I thought it might be the file I was trying to print - it failed 3 separate times on the same file...but others would print fine. chatted with knowack last night about it, he even offered to try printing the file I was having a problem with...

I turned on the log save function in RH so it would save a copy of the log as a txt file so I could review it after killing everything when this happens...

this morning, I fired everything up, started the bed heating - had not even loaded a file yet - and it quit responding again - bed was still heating but nothing working in RH... had to kill power to the printer, and shut down RH the hard way (task manager>end task)

the 12.18.15 RH crash 1 file is from that instance...note the last line - "communication timeout"

moved the USB cable to another port on the computer, rebooted everything, and tried again...

heat bed, so far so good...
load a file and slice - still working...
bed is ready, heat extruder - all is well so far...
start print - and it starts printing fine...
then suddenly it stops dead in it's tracks... print was about 2/3rds of the way done - printed a copy fine last night.

Well poo.... kill everything again, and go dig up the log (12.18.15 RH crash 2) - hmmm, "communication timeout" thing again.

so - anyone have any thoughts about this one?? I am at a loss as to why it would work fine for a couple of weeks and then suddenly start crashing left & right

FWIW - I have triple checked baud rate settings - all instances are the same - COM port, RH connection settings and firmware - all set to 115200 as this computer only goes to 128,000 in the COM port settings.

This is on a Windows 7 pro, 64 bit, dual core processor machine with 12gig RAM, the USB port is straight off the motherboard - no card, not a hub.
Printer is my #1 SD4 running on the Rumba board...
other than various slic3r settings changed, I have made no other changes to the setup since updating RH.