As of SEP 12.1 RU1, a detection was implemented in the install process which will prohibit installation if the Base Filtering Engine service is stopped or its registry keys are missing/corrupt.
The Base Filtering Engine (BFE) is a Microsoft service that manages firewall and Internet Protocol security (IPsec) policies and implements user mode filtering. Stopping or disabling the BFE service will significantly reduce the security of the system. It will also result in unpredictable behavior in IPsec management and firewall applications. Symantec Endpoint Protection is designed to manage the Windows Firewall service and utilize the Base Filtering Engine service. Manually disabling these services is not necessary or recommended.
Intrusion Prevention in Symantec Endpoint Protection requires the Base Filtering Engine to be running. If the Base Filtering Engine is stopped, IPS cannot make detections.
This issue is known to affect both Windows Vista and Windows 7, 32-bit and 64-bit OSes.
It may also affect Windows 2008, Windows 8 and Windows Server 2012.