Jeeper wrote:
Duke

Many thanks for your prompt response. I tried your suggestion but,
unfortunately, without success. I still ended up with #N/A if any
cells in those to be added contained a #N/A. I tried to simplify the
prob into a small test as follows:

B6 6
B11 6
B16 6
B21 6
B22 Your suggested array formula

This worked OK and the result in B22 was 24 as expected . However If I
changed cell B21 such that it contained #N/A the test failed and the
result was #N/A in B22.

Woudl still appreciate any other ideas or things to try. Again many
thanks for your suggegstion.

with regards



If a large range is involved and every 5th cell is of interest...

=SUM(IF(ISNUMBER((MOD(ROW(B4:B300)-ROW(B6)+0,5)=0)*(B4:B300)),B4:B300))

which must be confirmed with control+shift+enter.