Sheeloo wrote...
Your workbook is probably still in XLS format... Excel 2007 imposes the
limits of 2003 in that format so that it can be kept compatible.
....

Compatible with respect to Excel formulas needs refined defnition.

For example, you could use OpenOffice Calc to create a formula with 20
levels of nested function calls, save the worksheet containing that
formula in XLS format (OOo Calc will issue a warning about
incompatible features), then open that XLS file in Excel 2003. Excel
loads the file and calculates the formula without problems.

I've tested this with the following formula.

=SUM(SUM(SUM(SUM(SUM(SUM(SUM(SUM(SUM(SUM(SUM(SUM(S UM(SUM(
SUM(SUM(SUM(SUM(SUM(SUM(A21,A20),A19),A18),A17),A1 6),A15),
A14),A13),A12),A11),A10),A9),A8),A7),A6),A5),A4),A 3),A2),A1)

You can change the values in any of the cells A1:A21, and Excel 2003
recalculates this formula without problems. The compatibility is in
Excel 2003's formula parser. While Excel will recalculate this
formula, it won't let you enter it or alter it, say, by changing the
reference to the corresponding cells in column D.

For this reason it seems odd Excel 2007 won't save such formulas in
XLS files and only issue a warning that users may not be able to EDIT
the XLS file in Excel 2003 and prior.

So let's not give Microsoft undue credit for greater limits in Excel
2007. For many previous versions, at least back to Excel 97, Excel was
able to recalculate formulas with more than 7 levels of nested
function calls in order to handle spreadsheets created by different
spreadsheet programs. Excel 2003 & prior could even save such files
after users made other changes. Microsoft just didn't bother to update
Excel's formula parser between 1985 and 2006 to allow Excel users to
enter or revise such formulas.