Turn on Logging (under Help tab). Perhaps you can catch the error and send to JRiver.
Also, check the logging under Windows Event Viewer. You may find the issue is with Windows. A recent automatic update caused my system to crash. I had to remove the update and reinstall MC to get everything stable again. Lastly, there have been problems with Microsoft Security Essentials program - if you have this, try disabling it to see if it is root of your problem.
Good luck.