I have the following formula.

COUNT(D4:D65536) which functions correctly.

a slight change

COUNT(D4:D65537) does not work.

To summarize if the range is greater than 2^16 then it seems to be
overflowing the system. The Max worksheet size is 1,048,576 rows by 16,384
columns according to the documentation so why doesn't this work and there is
a way to get it to work? Same result in Excel 2007 and 2003.
--
Tim