Today I ran into the phenomenon that an Avamar cient suddenly coudn't connect to the Avamar Server. If you run into this problem where “re-registration" is not permitted and you get the error Avamar Client Activation Error do the following:
Login in your Avamar Administrator > Activity. You see the below message.
On your client you see this error while trying to re-register
Open the Avamar Administrator > go to Policy > Edit Client > Uncheck the option “Activated”. Then retry to re-register the Avamar Client.