We've deployed Office 2007 on over 150 machines here, and only 1 user
is having this problem.

I've changed her default save format to the 97-2003 format, and it
works just fine for the day. At the end of the day, she logs off of
Windows, and the next day she opens Excel, and sure enough, Excel
automatically changed the default save format back to 2007. She
shouldn't have to change that every day. Any suggestions?