Very odd one this and am not holding out much hope, but then you never
know.

We have a massive spreadsheet we use that was fine until a user tried
to get into it last night and received the following error:
Now we cannot access the file at all, I have managed to restore the
previous nights backup, but they have lost a ton of work that was put
into it yesterday.

The file size has also changed from 3Mb to 512Kb, which is very odd.

As I said, I am not hopeful on this one, but if someone can help it
would be greatly appreciated.