Please see this wiki article that list the most common errors in Argon communication. That error probably is caused by one of the listed reasons:
http://granitedevices.com/wiki/Device_connection_troubleshooting

The Granity crash is probably completely different issue and it has happened for me too (rarely). This is on the fix list. If you can figure out how to repeat the crash, then description of it would be a great for pin-pointing the bug!

If settings disappear from the device, is caused by quitting application or disconnecting without saving settings to the drive. See:
http://granitedevices.com/wiki/Granity:_Connect#Loading%20and%20saving%20settings

My first steps with the granity soft and argon driver
I started to use a DC motor
and a rotary encoder quadrature TTL 250 points (directly attached to the motor shaft)

I set the first time the torque response with MR and ML parameter up to an acceptable response

I then made settings in position with the encoder
the error message started to appear on comunication and a loss this link with argon
Communication error flags:
*Communication (cheksum mismatch)
*DataLegth (timeout or app error)

I stopped with argon estop and reconnect the driver with the conect menu
for continued testing but the same error message appeared
This continued even after reboot several times with argon

I then replaced the ethernet cable to try to continue testing
I did not find the error message with this cable.

I continued testing and setting up an exellent resulta
but in the end when I no longer touched the soft parametrage the Granity is closed as a crash without error message!

I also noticed that all the parameters are not always stored in argon and return to default values

thanks