Try the following steps
1. In the main SEPM, go to Start > Run > cmd, click Ok
2. In the command prompt execute netstat - abn
3. Check that SemSvc.exe is not listening in the default port (TCP 8443)
4. Go to the SEPM installation folder c:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\conf
5. Open the server.xml file and take note of the last port mentioned in the file (default is 8443).
<Server debug ...>
...
<Service name=...>
<Connector acceptCount ... minProcessors="5" port="8443" scheme=" ...>
6. Execute again steps 1. and 2. and assure that SemSvc.exe is in Listening state in the port which is configured in the server.xml (step 5.)
7. Run the "Add additional Symantec Site" installation wizard with the port found in the server.xml file