Entourage 2008 Group email error

I recently upgraded a user from Entourage x up to 2008. She has a lot of 
groups and they did im****t over. It seems now some of the groups will get
an 
error when trying to send email to the group. The errors are
5.1.3 Bad Recipient Address Syntax and at the bottom Error -17099. i 
researched these and it says it is a bad address or the ISP is not
allowing 
it. The groups worked fine in Entourage X. Some groups have 5 people and
some 
have up to 25. Have had the error in both. The odd thing is if I send the 
email to each individually it will send. The groups have the right email 
addresses. Also have rebuilt the database and it does the same thing. I 
wanted to know if there was any other ideas before I have to redo all
these 
groups. That was my only other thought.
Thanks