Error when using Autodesk Revit Architecture 2012

Hi,
I was using Autodesk Revit Architecture 2012 when I got this error message (see below).
I was trying to copy a selection of drawings when the error happened. I have searched the web, but no one has yet encountered such problem so this site might provide me or help me find a solution.
Thanks in advance.

Autodesk Revit Architecture 2012
Error – cannot be ignored
Selection cannot be copied.
Multiple instances of the same view in sheets not supported.
