VLOOKUP Works In 2K3 And Breaks In 2K7

I have a file I inherited that uses many VLOOKUP formulas. It was written in Excel 2003, and works perfectly there.

However, I just had to install Excel 2007, and when I open this file, all those formulas return #VALUE! errors.

Is there a known issue with VLOOKUPs in 2007 versus 2003?

An example of one of the errored formulas is:

=VLOOKUP($C3,ItemMaster!$A$1:$N$5800,2)

It should be noted that the first row of this range is the column titles, rather than data. But as I said, the formula works fine in 2003.

What's completely bizarre is that if I edit the formula to either of the following, it works fine:

=VLOOKUP($C3,ItemMaster!$A$2:$N$5800,2)
=VLOOKUP($C3,ItemMaster!$A$1:$N$5800,2,FALSE)

Changing the first row of the range to row 2, or adding the FALSE at the end makes it work. But why would it work in 2003 and not in 2007?

This is an *enormous* file, and this is just one example of a *load* of formulas that are returning errors (so far, all seem to be related to VLOOKUPs - at least the ones I've found so far). It's 25MB worth of complicated formulas, with external links to Access databases for the source data, just to give you an idea of the scope. So going through and trying to find and then change every error that might be occurring just because 2007 doesn't like it is going to be a complete disaster. You never find them all. It might be simpler to just downgrade back to 2003!