The error message you receive tells you what's causing the problem. Read the
error. If you can't figure it out, post the full text here, but be sure to
alter and real mail addresses it contains so that you don't give away any mail
addresses to the spammers who troll for addresses.
The most likely problem is that you've misspecified one or more addresses in
the Distribution List (if that's what you mean by "group", since Outlook
doesn't have anything called "group e-mails").
