A 10 second google search found this:
http://support.microsoft.com/?kbid=138275


"saved workbook trouble" <saved workbook
wrote in message ...
: two people are working out of this workbook, but saving changes and
: forwarding via email. This time the saved workbook is being renamed scrap
and
: the email attachment reads with an .shs extension. The second person
cannot
: open the document.