LOL -- still don't know which script to test ("Artwork-Selected to Album in Playlist" or "Artwork-Add Found to Each Album in Playlist"? ;-)
IIRC, the out-of-memory error occurs when a script tries to grab track art that doesn't exist; there may be more cases where the same error occurs.
Applescripting art has never been a very smooth thing in iTunes, but the logic in those two scripts looks OK in a quick read... Maybe you should test again, keeping this in mind -- the "Artwork-Add Found to Each Album in Playlist" script isn't looking at the tracks you've selected; it's looking at the playlist that's being displayed. So if you've got your Music listing displayed and have one track selected, the script is actually trying to process every music track you've got -- that may just be too much of a load.
If you're using the "Artwork-Add Found to Each Album in Playlist" script, try creating a playlist with just one track in it, and see how that goes....