Cannot Read File

See: https://musescore.org/en/node/52116
HTH

Your file seems to be corrupted. The mscz file is --should be-- a zipped file, so appending .zip extension and opening it with any unzip program should yield a .mscx file along with two folders. In your case unzipping fails, which happens when the file is corrupted.
Probably, if not much file work has been done from the time the file was corrupted, might be some recovery is possible. A favorable situation would be if your MuseScore settings include saving a backup version, which can be recognized because it starts with a dot and ends with a comma, for instance ".Kessingland Suite.mscz," (without quotes).
If not, I'm afraid there is little that can be done. I suggest that in the future you enable this, but a still better idea may be to save important scores both as .mscz AND .mscx files, since the latter is a text XML file that can be manually recovered, at least partially. Even better, once in a while, you can save your work under a different name, and still better, on a different medium (a pendrive, a second HD unit). A corrupted zip file is usually unrecoverable since the information may be scrambled and is definitely unrecognizable behind a lot of binary data.

See also #271185: Scores corrupted beyond repair, containing nothing but zeros

I confirm your .mscz file, as is, is unrecoverable since it has a brief header and then follows a long string of zeros (no information). If there is no backup copy around, the only hope would be that the information is still on the HD but the file system cannot find in because of some bad pointer o so, and thus replaced it by zeros to keep the file length as reported. It would take a very knowledgeable person to recover it.