If I use XL2007 to open an XL2003 file which uses Networkdays() it appears to
work OK. BUT, when I save the file (as .xls) it corrupts the formulae. The
worst part is that I get no error message on saving, but the next time I open
the file with XL2003 or XL2007, I receive the message: "File Error: Data May
Have Been Lost". If I look at the Networkdays() cells, the numbers (values)
are still there but where there used to be a Networkdays() function, I now
see "=#N/A"!

This is where it gets weirder. If, when I first open the file in XL2007, I
then save it as .xlsx or .xlsm I can re-open it with XL2007 and the
Networkdays() formulae are still working - Great! Not just that, but if I
save it, from XL2007, as .xls (XL2003 format), I am able to reopen it in
XL2003 or XL2007 and I don't get the aberrant behaviour any more. At least I
haven't recently (fingers-crossed!).

This has got to be a BUG, but I see no mention of it in the KnowledgeBase
and nobody in the Community seems to have a solution. Any new leads?

Sean