So if you pick the group using the people picker, the form saves, but when you populate the fields using rules it fails? If that's the case, I'd put a repeating table on the form bound to the people picker repeating group so you can see the values being set when you use the people picker vs. your rules. Sorry I don't have other suggestions, it just isn't any thing I've needed to do before. :)
Hilary Stoupa
