The error ARX_ERROR: eDuplicateKey can occur if you are working with a file that was saved in the 2004 or earlier DWG format from a 2007 based product. This error is caused by the presence of more recent version of AEC objects that are too complex to save back to an earlier drawing format.
Three Object Enabler Hotfixes have been released to prevent these errors.
For AutoCAD® 2004 or 2004 based products:
For AutoCAD® 2005 or 2005 based products:
For AutoCAD® 2006 or 2006 based products:
Drawings with custom AEC objects created in an AutoCAD® 2007-based product and saved in the AutoCAD® 2004 or older drawing format may display multiple error messages when working with them in an AutoCAD 2005-based product. This Hotfix suppresses the unneeded error messages.