Tried a "save as" today with my usual settings (JPG, preserve EXIF, rename with "sm{filename}", apply crop, scale to fit 800 px box, 72 ppi, sRGB, use JPG) and got an error message before the first selected file was converted:
"There were errors during the Save As operation."
Very helpful.
Any clues as to what could trigger this message? Plenty of room on destination disk.