I get this message when attempting to pack all textures. My actual question is: How to easily locate those "unsaved" textures?
I did this before with a copy of this file and there were no problems. The difference this time around is that I packed some textures individually. Then I went to the File menu and chose External Data/Pack all into .blend.
Thanks guys,
DPC

F3) and there's unsaved paint since then, you can use UV/Image Editor > Image > Save All Images. – Mr Zak Mar 27 '16 at 23:07