A little more info I just found out...

The file is a .xls instead of the native 2007 version .xlsx

When asked why they would save the file in a non-07 format, she said that
the client that she was emailing this file to each day doesn't have Office
2007.

Also, there are no macros, but there is a security warning on the
spreadsheet that says, "Automatic update of links has been disabled."