I regularly get this error message when I try to save changes to an existing file.
I can use 'save as' and then delete the original but this is a pain as I have to do it with virtually every image.
I do have admin permissions and Photoshop opens the file without issue.
It only happens after I make a change (even a minor one)
Does anyone have any ideas?
You may try few things to fix this issue.
Please change the location where you saving the file now
Check the read and write permission for the file folder
Reset Photoshop preferences back to defaults and check if that helps. refer: Preferences in Photoshop