3.Once the login is accomplished, the CMS sends its SSL certificate to the agent on the managed host, and the agent supplies its SSL certificate to the CMS. Application Discovery agents can now transfer data securely to the CMS, and the CMS can authenticate the transmission.

Have you recently restored or removed and reinstalled the CMS? :

A restore or removal of the central management server also removes the certificate recognition previously established between Application Discovery server on the CMS and Application Discovery agents on managed nodes. This relationship must be re-established when the CMS is reinstalled or restored by completing the Application Discovery certificate exchange.

68 Completing certificate exchange