Well, I've checked the Reference Libraries for the 2010 and 2013 installations. Excel 2010 has version 14.0 and 2013 has version 15.0 (as I would expect). I don't know much about these libraries but from what reseach I've done, it seems that the version 15 cannot be installed in Excel 2010 and version 15 which is in Excel 2013 should already be compatable with the version 14 library. So I don't think this is the problem. As I said in the orginal post, the errors I get from Excel 2013 are on very basic commands like activating another loaded workbook. My thought is that since Excel 2013 handles workbooks in seperate instances of Excel, they might have to be addressed differently in the macro (something more than just (Workbooks(1), Workbooks(2), etc..). I guessing that each instance of Excel is using Workbooks(1) since they are seperate. I can't get onto one of the computers with Excel 2013 to test any of these theorys. Can anyone using Excel 2013 verify this?