It doesn't work either in MediaMonkey 4. I've added it as: http://www.ventismedia.com/mantis/view.php?id=7525

Sounds like a problem with the script or the scripting API.
Normal usage doesn't give me any errors.
It is allowed by MM and I think it should be.
For example, a auto-playlist may use a combination playlists and making them it's child saves visual space and denotes correlation.
So the ''Send to' should allow you to send items to the child playlist. Of course, not to the parent auto-playlist.

Because it won't work with some scripts. Ex.: http://www.mediamonkey.com/forum/viewto ... 15#p246823

Auto-playlists are allowed to have children.
Create an auto-playlist
then right-click it, and select 'New Playlist'
Now it has a child.

You say this shouldn't be allowed?

Children of auto-playlists?
Auto-playlists should not have children. Regular playlists could.

Otherwise it won't work with some scripts. Ex.: http://www.mediamonkey.com/forum/viewto ... 15#p246823

Send to should be able to send items to normal playlists that are children of auto-playlists
MM 3.2.4.1304