Actually I do not think this is an excel 2010 thing. Prior to upgrading to 4.1 excel would give a warning but would open the file.
Since upgrading to 4.1, the xml produced by the formatter is no longer valid xml. For example
Cleaning up the dupes and removing the extra 0"> fixes the xml so excel is able to open the file again.Code:<ss:Alignment ss:Vertical="Top" ss:WrapText="1"/> 0"><ss:Alignment ss:Vertical="Top" ss:WrapText="1"/>
Trying to pin down in the Style.js file where the issue is.