source files showing as invalid or corrupt

My storyline 360 source files that I developed in 360 back in 2019 -2020 keep coming up with the message that the file is corrupt or invalid. It also says it may have been created in an earlier version of storyline but  have only used 360. It happens to a lot of them but not all.

I have to save the files on our network once completed and can't keep a copy on my C drive due to lack of space. If I need to update a file I normally copy it into my C drive before trying to open, but it only helps with a few of the files. Love some idea about how to stop this happening as it basically means we have to recreate the file to update it which is not cool at all :(

thanks all :)