Custom Function Fails When Row Hidden

Hi,

I have a spreadsheet that counts the value of cells in certain colours. This function works fine.

I then added a function to hide rows based on a cell value within the each row. On it's own, this works fine.

With both functions in the file the colour counting function still works, unless I hide rows. For the hidden rows the colour counting function fails. However, if I hide the rows manually, everything works fine.

For added complexity I need to do this on two platforms:

On a Windows XP system running Excel 2003 all the relevant rows are hidden, but the colour counting function does not return a value

On a Mac running Office for Mac 2011 (Excel 2011) execution stops at the first error, with only the first row being hidden

I have attached the spreadsheet for reference.

FYI, I have added a forced sheet recalculation in the code, which on XP covers up the problem. However, this is not a long term fix; I need to get it working properly.

In any case, on the Mac the forced recalculation hack doesn't work at all.

Can anyone suggest why my colour counting function on a row should fail when that row is hidden?

Regards

Darren.