You may have just upgraded from Simpana 8.x to Simpana 9 SP2 or later and installed the Exchange DA Client on your Windows 7 client (x64) or Windows XP. Outlook is x86 version and Simpana 9.x Outlook Addin (MSI).
The Commvault documentation Install Using AD Group Policies just tell you in the last sentence that you need permission to Galaxy.Ex2KMBDM.CVEAAddin key. That sounds like a bad joke as it does not explain that you cannot set this value with a GPO together with the installation GPO and also not with two GPOs ordered one after the other (what Support suggested). The setup removes all it's registry keys and reinstall them later (also on updates over existing versions). To apply the permissons on the registry keys and folder you need to reboot the machine after the setup has been completed. But the setup does not reboot itself as there have been no files in use that require a reboot. Now, try to explain this reboot requirements to a few hundred users...