Mailing to Group inMS Outlook

I have used Outlook Express for years, but people have told me I should change over to MS Outlook. So, I did… exported all my folders, address book, e-mails, etc. over to MS Outlook. Now I’m trying to forward e-mails to one of our groups and I get an error message saying “An internal support system returned an error.” I’ve forwarded to this group in Outlook Express with no problems. I’ve gone through every option I can find to see if I need a setting changed. Can you help? Thanks, Ellen & Mark Anthony