Could you check following article

After the Symantec Endpoint Protection 12.1 installation, the firewall driver is not loaded. Cannot uninstall NTP (Network Threat Protection)

http://www.symantec.com/docs/TECH166169 

Also you can try following steps,

Remove the  Network Threat Protection (NTP) component, then reboot the machine and install it again.

1. Control Panel > Add or Remove Programs > Symantec Endpoint Protection > Change > Modify >  Network Threat Protection > Entire feature will be unavailable.
2. Reboot
3. Control Panel > Add or Remove Programs > Symantec Endpoint Protection > Change > Modify >  Network Threat Protection > Entire feature will be installed on local hard drive. 

Added some more..

Check this forums also

https://www-secure.symantec.com/connect/forums/sep-121-firewall-malfunctioning-firewall-driver-not-loaded-0

Hello Shahram,

Please check if uninstallaing and reinstalling only the NTP works. If yes then you can add a package to the groups without the NTP so that the NTP would be removed from the the clients once it is done then you can add a package with NTP to the group again and that should fix the issue.(Removal of NTP requires a restart)

Please follow the link below to add and remove client features:

Hello,

Check these Threads below with similar Issue - 

https://www-secure.symantec.com/connect/forums/symantec-121-firewall-driver-not-loaded-error

https://www-secure.symantec.com/connect/forums/sep-121-firewall-malfunctioning-firewall-driver-not-loaded-0

Check this Article:

After the Symantec Endpoint Protection 12.1 installation, the firewall driver is not loaded. Cannot uninstall NTP (Network Threat Protection)

http://www.symantec.com/docs/TECH166169

Hope that helps!!

Try upgrading to SEP 12.1 RU1 Mp1

Regards

Please do the following

Use CleanWipe to uninstall the SEP 12.1 client

Upgrade Internet Explorer to version 8 (IE8)

Reinstall the SEP 12.1 client.

Regards

Hi, Shahram

Please Update us, If you did somthing there that worked.

It will be helpfull for us too,

Wish luck,

Thanks ;)

Still an open issue?

Hi Dushan

You can directly upgrade to SEP 12.1 RU1 MP1

Regards

I had this problem with 12.1 RU2. I thought I'd add my fix here in case anyone else is still having this issue.

To clarify, this was with a standalone package install. After reading this thread;

https://www-secure.symantec.com/connect/forums/sep...

I tried to load the driver manually by adding it to the LAN adapter. I got an error saying that there were too many filters loaded. So, I removed Virtual PC Network Filter Driver and then installed the Symantec driver. The Symantec Firewall driver was in the list already but if not I believe you can install it from

C:\Program Files\Symantec\Symantec Endpoint Protection\12.1.2015.2015.105\Bin\TeeferVista

Once rebooted the Firewall was working. Of course, if you need the Virtual PC Network Filter Driver, you might need to remove a different one and have a shout at Symantec.

Cheers!