Invalid archive file analysis/diagnosis

[TimOliver]

I get a lot of support emails and 1-star reviews saying "It won't open my files" without additional explanation, and the best I can do is try and follow up with them about where they got the file from.

One potential way to mitigate this is to maybe replace the "Could not open file" error message with one that attempts to ascertain exactly why the operation failed (invalid format, no valid files inside, archive is corrupt etc) and to explain that to the user.