Symantec Endpoint Protection Manager (SEPM) Find Unmanaged Computers Client Install Fails on Windows 7

Symantec's reason why it fails:

When you logon to the A machine as administrator the SEPM runs using the local sysytem account. In the Windows Server 2008 r2 if you try to deloy any SEP package using local system account from SEPM ,it will not have the access to Remote registry of the client and you will get "Access denied" which can be seen in the logs. Therefore running the SEPM using the Administrator Credentials for SEPM services manualy will give access to the remote registry of the client.

How to fix this:

Click Start -> Run -> Type services.msc -> Scroll down to Symantec Endpoint Protection Manager ->
Double click the service -> Click the Log-on tab - > Select This account fill out your information.

Click Ok and restart the service.  This should now work on the machines it was failing on.

Source:  Link  Link