Data has been lost - some of the ATP functions will have been
overwritten with =#N/A, and the calc chain could have been corrupted
across multiple cells.
more info here:
http://smurfonspreadsheets.wordpress.com/2009/02/23/excel-2007-na-error/
Best fix is move to .xlsx or .xlsm formats, only save to .xls to send to
people without 2007.
Cheers
Simon
Excel development website: www.codematic.net