I was trying to add my laptop to my local Veeam Backup & Replication server but was unsuccessful in adding it to a protection group. The error I received was:

Veeam Guest Credentials test failed: rpc connection failed

First I tried all the obvious… Adding ports to the local firewall… Disabling the firewall… Testing the connection with PortQry… Nothing worked! Even connecting to the c$ share wouldn’t work. But wait, the user account I am using is a local administrator. So why is that connection to c$ not working?

The answer is LocalAccountTokenFilterPolicy. This is part of the User Account Control Remote Restrictions. This mechanism helps prevent against loopback attacks and also helps prevent local malicious software from running remotely with administrative rights. For more information please check the Microsoft site.

After adding the registry key to the local laptop I was able to add it to a Protection Group. Case closed!