I messed with this for days until I found a simple and elegant solution at:
http://glowicki.pl/02/27/symantec-end-point-protection-sbe-firewall-driver-not-loaded-malfunctioning/
I have Windows 7 64-bit workstation SP1. SEP 11 was installed on this computer and it worked perfectly. I uninstalled SEP 11, ran the WipeClean Utility and installed SEP 12.1 unmanged. That is when I got the "Firewall driver is not loaded" error.
I removed the computer from the network domain before I found the final solution, so domain removal may or may not be mandatory. I tried lots of uninstall/reinstalls. I did a custom install and excluded the Network Threat Protection -> Firewall. I turned off the Windows Firewall when I installed SEP. Nothing worked and none of the prior posts in this comment worked.
I could see the problem with my system was the Symantec hardware device driver would not load. I opened Hardware -> Device Manager -> View -> Show Hidden Devices, then expanded Non-plug and Play Devices. One of the Symantecs driver had an exclamation point error symbol. I deleted the device, scanned for hardware changes but Windows would not find it to rebuild.
After I read the forementioned blog, the final solution was so easy.
1) Uninstall Symantec End Point Protection client from the computer. For safety I also ran the Symantec Wipeclean Utility.
2) Run -> regedit
3) Teefer 3 is a leftover (I think) from SEP 11. Delete the following four keys of SEP connected to the old Teefer3 driver.
HKLM\SYSTEM\ControlSet001\Services\Eventlog\System\Teefer3
HKLM\SYSTEM\ControlSet002\Services\Teefer3
HKLM\SYSTEM\ControlSet002\Services\Eventlog\System\Teefer3
HKLM\SYSTEM\CurrentControlSet\Services\Teefer3
4) Reboot.
5) Reinstall Symantec End Point Protection. If you examine the above four registry key locations where Teefer3 once resided, you will now see keys for Teefer2.
Good Luck~!!