Problem
If you attempt to edit the authOrig attribute of a mail enabled group using ADSIedit you will get the following error.
Solution:
Use PowerShell
You can (if you have no access to Exchange Management tools) simply use PowerShell, the syntax is as follows.
Set-ADGroup -Identity "The-Group" -Server The-Domain-Controller -Add @{authOrig=@('The User or Group to Grand access to')} e.g. Set-ADGroup -Identity "CN=DG-Test-Disty-Group,CN=Users,DC=pnl,DC=com" -Server PNL-MGMT.pnl.com -Add @{authOrig=@('CN=Pete Long,CN=Users,DC=pnl,DC=com')}
Then to verify, you can go back to ADSIedit and check.