Excel fomula not evaluating correctly

I've got a spreadsheet here with a simple set of calculations. Basically each column is summed, then that row is summed at the end.

The columns are summing correctly, but the total at the end just returns 0 all the time.

We've checked that the cells are formatted as numbers/general, we've checked calculation is on auto. If I go into edit the formula and click the 'Calculate Now' button, it calculates correctly, and overwrites the formula with the result.

What on earth is going on?

Any chance of uploading file? (To show/test issue I mean). Whether it's real data or fake, just nice to be able to see it :)

Steve