Have you tried turning it off and back on, again? Then once more?
Does the 'ESC' key work in other applications?
Does anything appear at the command line when you hit the ESC key?
Are you sure Autocad is the application 'with focus' when you're trying to cancel a command?
Can you check and see if there is a different command mapped to the ESC key?
Can you check and see if the 'cancel' command has been removed from the 'ESC' key in the CUI?
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5