I don't know whether this is the right place to ask questions about the Halo extension. I couldn't find separate contact information for that extension, so I'm sending to this list; if there's a better place to send Halo questions, please let me know.
Anyway, I tried setting up the Halo extension today, and it looks like it's inconsistent with SMW at the moment. It requires SMW's "/includes/SMW_Datatype.php", which is a file that no longer exists; the version of SMW that comes pre-packaged with Halo doesn't seem to contain it either.
Is Halo essentially out of date right now?