When the default preference is to save all Excel 2010 workbook
in file format of Excel 2003, change the ‘Save files in this format:’ on the
Save sheet options, to Excel 97-2003. File extension of Excel 2003 is *.xls File extension of Excel 2010 is *.xslx
Click File TAB, Options, Save, Select the preferred format
in the ‘Save files in this format:’ field.