Are you trying to replace a .xls with a .xlsx?
If yes, we do NOT support it in 2010 release, we only support replace with the same extension file name.
We will take it into account in the future.
I'm trying to edit the spreadsheets for various iParts, and all Inventor 2010 does is blink and change the context menu to "How to..." It never actually launches Excel, and I have to press Esc to get my context menus back to normal. If this is a problem with compatibility between .XLS and .XLSX files, how do I fix it? (I'm on Windows 7, if that makes any difference.)