Copy and Paste is very dependent upon the Microsoft "clipboard" functionality. If you are having problems, first try exiting SOLIDWORKS and restarting in case some communication between SOLIDWORKS and Microsoft has started failing for some reason. If that does not work, try rebooting in case there is something wrong with the MS clipboard.
Post back whether either of those worked and if not, try a simple case to see if there may be something specific about the particular things you are trying to copy/paste that are causing the problem.
Pure genius Jim! You could work for cable or ISP tech support! Rebooting worked. Don't know why I didn't think of that...