Try to turn on the tamper protection.
Maybe this is being done by a VIRUS

 Are they managed?

Yes they are. sometimes they will go green, but most of the time they just stay red. Are they waiting for some command from the server to change. On the Mgmt Console all these clients show communication and green lights.

Hi Kweler,

I hoe you are using the latest veriosn of SEP 11.0 MR4MP1a.

If not , then try to install the same on aroud 2-3 machines and check the status.

Also I woould recommend you to update the machine with latest RR dfinition and scan them in SAFE MODE with System Restopre OFF. Take 2-3 machines and see the results.

Further , if you contact technical support team, the first question which they will ask is about the version.

Rgrds,
SAM

Hi Kweler,
     For any client that is indicating a non-OK state (non-green icon mask on top of the SEP Tray icon in the Taskbar), please try to identify what is the exact problem that the client is reporting.

For any such client persintently showing any problem, if you mouse over the tray icon, the tooltip will indicate what the possible problem is. If there are more than one problems, you might have to open the Client UI to get details of the specific problems.
Possible problems could be Out-of-Date definitions or certain technology not working. Please report what you see.

Regards.

Try to re-enforce the policies and run update command

Is proper sylink.xml you installed, please check and update.

 Once you open the client program, typically some warning showing the error also is shown. Most issues happen with out-of date definitions. 
What about connectivity? Are you having problems resolving names to IP addresses? You can also push policies again on the client and see if it picks it up. If all else, try re-installing

may be there is some virus related issue. suggesting you to download & update rapidrelease version & scan your pc in safe mode once.

Is your file File System Auto Protect enabled? Also you can go for checking the Tamper Protection to enable.

Please run the SEP Support Tool available on Symantec Website. It will provide you troubleshooting details (network, softwares..etc)