Syncing issues - "not more than 5 iTunes accounts"

Question

I just received, activated and synched my new iPhone4. Activation was a breeze, but when I tried copying music and a couple of movies from my iTunes library, I got the message:
"Some of the iTunes Store files in the iTunes library were not copied to the iPhone because the iPhone may only contain content from five iTunes Store accounts."
I ran the Track Down Purchases script (from Doug's Scripts) on my entire library, which revealed one song from a sixth account that I then deleted. I re-synched but got the same message as above. Quitting out of iTunes and then re-launching made no difference. Short of looking at each song individually, is there another approach for showing account ownership of purchased iTunes music that might reveal additional problem songs?
Also, does anyone know a way to show which account purchased which songs in my iPhone library? The Track Down Purchases script works only my computer's iTunes library, not the iPhone's (or iPod's).

Answer 1

I did that with my 3GS before ever starting the activation process for the 4, having gotten the not-all-your-iPhone-purchases-are-in-your-library message when I did one last backup of the 3GS. I then activated the 4, synched, got the 5 accounts message, ran Doug's script, deleted the song, and re-ran the script with no additional accounts showing up (though I can't remember if the second pass-through was before or after re-launching iTunes).
Weirdly, when I later tried to erase my 3GS, I again got the message that not all the songs purchased on my 3GS were in my iTunes library. I did the file->transfer purchases two more times and kept getting the not-transferred message and finally just erased the thing.