Hello,
Check if the client is properly communicating with the SEPM.
I would suggest you to please Repair the SEP client from the Add/ Remove Programs of that machine OR / AND please replace the sylink.xml file on the client machine.
Secondly, check this Thread: https://www-secure.symantec.com/connect/forums/symantec-121-ru1-missing-tray-icon
To hide the shield icon we will need to add the following registry (dword 32bit) and set the value to 0 (1 for showing the icon)
HKLM\SOFTWARE\Symantec\Symantec Endpoint Protection\SMC\LaunchSmcGui
You will need to restart SMC service before you can see the effect.
Hope that helps!!