"changes to the public group membership cannot be saved" error from Outlook 2010 users, but no problem with Outlook 2003.

We have the exact same issue as this but our groups are already universal security group and we still have problem:

http://social.technet.microsoft.com/Forums/en-NZ/exchangesvrmigration/thread/2c953cb4-5411-4f72-beb9-6b4c16fd6685

The distribution-groups were upgraded to Exchange 2010.  User A can update the group from Outlook 2003 or OWA 2010 but not from Outlook 2010.  Anyone know the solution?

thanks