KB ID 0000603
Seen On Exchange 2010 (SP1), when trying to add a user to a distribution group.
You don’t have sufficient permissions. This operation can only be performed by a manager of the group.
1. There a few reasons for this error, I’m assuming that there is no user set as the manager for this group? (Properties > Group Information > Managed By). In my case it’s a known bug in Exchange 2010 with SP1.
2. This was fixed in Rollup 3 for Service pack 1 (source), Simply run an update and the problem should cease.
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