If the suggestoin from above will not help, you can create and post here the communication log from the client. It will be helpfull for the communication troubleshooting:

How to enable Sylink debugging for the Symantec Endpoint Protection 11.x and 12.1 client in the Windows Registry
http://www.symantec.com/docs/TECH104758

Hi,

I would suggest to isolate issue first.

Replace Sylink.xml file on 2-3 machines & check green dot stay connected or not ?

If yes & if it's possible try to replace sylink.xml file on all the clients.

If not, collect sylink monitor log from two worksations.

One moe thing, have you run management server configuration wizard after doing all these changes ?

Hello,

Could you let us know the OS installed on the SEPM server?

Is the SEPM sync with Active Directory?

This issue occurs when a Symantec Endpoint Protection (SEP) client is registered in the Symantec Endpoint Protection Manager (SEPM) with a Group ID for a Group that no longer exists. This happens most frequently in environments using Active Directory Synchronization.

Could you try replacing the Sylink.xml files on these computers and check if that resolves?

http://www.symantec.com/docs/TECH165321

Also try:

Troubleshooting communication problems between the management server and the client

http://www.symantec.com/docs/HOWTO55017

Troubleshooting communication problems between the management server and the console or the database

http://www.symantec.com/docs/HOWTO55032

Hope that helps!!

Finally,

Please also try to repair SEPM too.

Regards,

Oykun