Hi, the issue may be connected to the naming convention - I was able to recreate the issue. While I'm creating/working all the images being accessed/used are held on the desktop (mainly for quick convenience and I can see them visually), I also use a leading prefix ie: AATheClouds so all files/images appear at the top of a desktop list - if I change the .affn file prefix on the desktop from say AA to BB - when I later try to close the Affinity File I get the 'Failed to Save document' problem. This may be happening in Designer as well. My solution is to Save and close the .affn file THEN rename it and open it from source location.