I am working in AutoCAD 2013 (HydraCAD extension) and I cannot copy and paste. Not with the right click selections, not from the edit tool bar and not from the "standard" toold bar with the copy and paste options.
This file has many xrefs but even when they are removed for the time being, it still will not work.
It however work from a brand new "drawing 1" file.
Any ideas whats up? This has been very irritating when I cannot even copy sinple lines from one drawing to another.
Can you try resetting AutoCAD?
http://upandready.typepad.com/up_and_ready/2012/07/the-easiest-way-to-reset-autocad.html