Resolution
Why does the remote registry service need to be turned on to install agents?
fix
The Agent Manager needs to access the registry of a target computer to collect computer attributes (computer characteristics that are typically defined by a registry key or value). The Agent Manager evaluates the computer grouping rules (which are defined by the attributes) to find all computers with a specific attribute for inclusion in the corresponding computer group.
Many of the API (Application Programming Interface) calls for the attribute collection process depend on the remote registry service being enabled. Failure to have this service started at the time of an Agent Manager scan will result in the failure of the scan and any process that depends on it.
This service does not need to be enabled for manually installed agents that were installed with the 'No Control' option. With these types of agents, the process of computer grouping is handled manually. Therefore, the remote registry service does not need to be enabled.
Note: Security Manager version 5.5 does not use control levels. Nonetheless, you do not need to enable the service when using a manually-installed unmanaged agent.