[dasymington]

Eventually, by first going to an item not in the tree above the imported Excel item, I was able to view items in the database without the error pop-up and then, when I tried the affected item and the tree above it, I could access these items again.

Panic's over ... scary experience, though.

There does seem to be something wrong with importing documents like this. I can email the spreadsheet I was importing, if that would be any help, although I've tried it with a test database and it imported OK. I notice, however, that the text in the item pane is not complete, but when I open the stored document the full spreadsheet appears to be there.