Hello,
You have Installed Symantec Endpoint Protection Manager on XP SP3.
Check this Article:
http://www.symantec.com/docs/TECH91694
You are installing the Symantec Endpoint Protection Manager (SEPM) on a Windows XP machine. Windows XP has a 10 concurrent connection limitation that has been built in by Microsoft. This guide contains the configuration changes that are necessary to work around this limitation. This is supported for up to 100 clients managed from a single XP SEPM
Could you please Let us know:
1) If you have Restarted the machines after SEP got installed?
2) What do you see if you open the SEP client, Click on Help and Support, Click on Troubleshooting. What do you see next to "Server"??
Suggestion: Please Check the Article above and work on the steps provided in the same.
Hope that helps!!