If you’ve deployed Exchange Server 2010 and have setup all your CAS server settings, your DAG is up and running. Your pilot users’ve been moved over and everything went well. Now your users are complaining that they can’t manage the distribution groups that they own. They were able to do it previously but now it isn’t working. Its because, you’re hitting an error message in Outlook 2007 when trying to manage groups (see first pic). So what does the “Changes to the distribution list membership cannot be saved. You don’t have sufficient permission to perform this operation on this object.” error mean, when you’re connecting to an Exchange 2010 server? It means Exchange 2010 is doing its job – as designed. Why’s it doing this? Exchange 2010 has quite a few features built in to allow your users to manage their own accounts and information. One of these features is the ability to manage distribution groups in a much richer format than Outlook 2007 provides.
Full Article: Exchange blog