Locked file

I recently downloaded Musescore 3. When I try to save a score that I edited in it, I get an error message saying "The following file is locked: [location of file] / Try saving to a different location." This has never happened before in any version of Musescore for me.

It also seems that I can't open the same file with Musescore 2, which means no backward or forward compatibility and I can't even close Musescore without risking the loss of my edits. Unfortunately I didn't save the original file compatible with version 2, which was a mistake on my part.

If anyone can help I'd really appreciate it.