Mp3tag consistently fails with a “cannot write file” error when embedding high-resolution album art (e.g., 3000×3000 PNG files around 5–15MB), even though this workflow has worked for months on the same system. Smaller or heavily compressed JPEG covers save successfully, but full-quality images do not. The issue occurs across all MP3 files, not a single file or folder, and standard tagging changes save correctly—only large cover art embedding fails.
I’m only using mp3s and I have been since I started, and seeing you did it is really confusing me because this was all the sudden it stopped working.
So it would be another direction to check what (else) has changed in the meantime.
Could it be that the files are also managed by a cloud synchronization program, e.g. OneDrive, Dropbox?