It is because you are saving to a different drive location and the autobackup of the file is causing the error.
Use File > Save a Copy As…
If the original file is saved in C: drive and then you save the same file in E: the link to the .skb is broken. Or something close to that.
You get the same error message when you try to save to DropBox/Google Drive etc but that is due to the .skb not syncing due to the latency in saving to the cloud.
Repairing the install as an admin / installing as an admin / running as an admin seems to help.
Don’t know much more, maybe someone with more knowledge will come by.