not able to expand the shared mailboxes with security group permission

Hi,
 
I am hoping that someone can help me. I moved some shared mailboxes from 2003 exchange to 2010. The permission to share were giving by the security group in AD. Now those shared mailboxes cannot be expand in outlook anymore. If I add individual user to the mailbox, then it is ok but not by the security group.
 
I have tried giving exchange servers full permissison to AD objects but still not able to see the result.
 
Hope someone can help me.
 
Thanks in advance.
 
cheers,