When I create a category in windows 8 live mail it wont sent to them.

I add the group name in the 'to' field,. It has a little + next to the category title,which shows all the member's emails when you press on it. However, when you press send it comes up with 'type an email recipient address in the to.. field'

If I add all the members  by hand it works fine.

What am I doing wrong?

Thanks