I have some Cisco 4510R-E that can't be found By CS Discovery. They can be 'pinged' from CW server.
IT is possible to add them manually, but not by the Discovery procedure.
The discovery is done by Ping Sweep On IP Range and the subnet for these 4510 is included. I have no problem discovering other elements.
My Cisco Works is a new installation of LMS 3.1.