I have a large workbook (size about 10 MB) consisting of about 40 sheets
summarised into about five sheets. When I change a figure in one sheet it
used to update the summaries. It has stopped doing that. The option is set to
auto claculation.

To update now I have to go into the formula cell by pressing F2 and press
return. Pressing F9 does not work.

What has gone wrong here and how can I resolve this? Your help most
appreciated. Thanks.