This is using x64 build 1530 on 7x64.
I have found a couple of times that when copying or moving files to a USB connected external drive I've run out of space on the target.
MC dialog reports no space & says I can abort etc but if I click any option or try to close the notification dialog with the corner 'X' it just loops back to the same dialog over & over.
The only way to terminate the process & stop the dialog appearing is to close MC completely.
