This article primarily focuses on environmental causes that can lead to this error. However, there is one possible cause that can be attributed to a configuration issue:
Attempting to add a machine to any protection group when it already exists in a protection group may cause this issue. Machines may be added to a protection group using either their hostname, FQDN, or IP. It is possible, but not recommended, to add a machine to multiple protection groups, but it must be done using the same identification method (i.e., hostname, FQDN, or IP). For example, the error will occur if a machine is initially added to a protection group using its FQDN and is later added to the same protection group or any other protection group using the hostname or IP address.
Another example of when this conflict might occur is if a machine was initially added to a backup job using the 'Individual Computer' option, which would result in it being added to the 'Manually Added' protection group. The conflict arises when a protection group is later created using a different identification method (i.e., hostname, FQDN, or IP). During the rescan of that protection group, the machine addition would fail, triggering this error.