When I try to save my workbook I get an error message telling me that 'Excel
could not save all the data and formatting you recently added to this
document'
To return to your workbook without saving it click Cancel, If you want to
continue saving changes without repairing click OK

So I click OK, but I'm worried when I close the page my changes haven't been
saved, although they appear to have saved OK. Clicking Help brings up a
blank help page - not very helpful!!

Any ideas why it might be doing this?