MS Office 2007 Excel extension .xlsx problem

I am trying to send a fax with an excel 2007 attachment of .xlsx

The error message appears that the format is incompatible?

Any ideas as to how to solve this?

MS Office 2007 has added a new formats to the file types, such as xlsx and docx. These formats are not yet supported
You can save any MS Office file to the 2003 format which for excel spreadsheet is xls rather than the MS office 2007 default format to xlsx when you click on “save as”.
This is also true with word documents - save as .doc rather than .docx.