“Invalid Project” error

Hello. In an effort to clear up clutter in Scrivener on my iPad, I moved some projects out of the Scrivener folder on Dropbox and into an archive folder. As I expected, they disappeared from Scrivener when I synced. But when I wanted to get back into one and moved it back into the Scrivener folder, it showed up again but won’t actually open—I get an “Invalid Folder” error.

Is there any way to get back in?

Thanks as always for a wonderful piece of software.

How did you move your project between Dropbox folders? on what device and using what app/software/UI?