Errors in the Windows Firewall

Error 0x8000FFFF
The Microsoft Firewall Service starts when Windows loads and is necessary for the firewall to operate. Error 0x8000FFFF is generated when the service cannot start and will be listed in the system event log. It will be accompanied by similar errors in the log file. This is specific to PCs running ISA Server 2004 or 2006. Microsoft attributes the error to a corrupted Web publishing rule in the Microsoft Internet Security and Acceleration Server (ISA) firewall policy. Fix this problem by first determining if the rule is, in fact, corrupted and then removing the problematic rule. Specifics included in the References section.
Service Termination
If you're not running ISA Server and the Windows Firewall still won't start, you'll see this error in the System event log: 'The Windows Firewall Service Terminated with Service-Specific Error 5.' This error occurs on Vista computers, and the firewall will fail even if you attempt to manually start it. 'Access is denied' summarizes the problem, with the fault lying with registry key permissions. The registry keeps track of each file and its location on the hard drive. The keys have 'permissions' that determine if they can be read, written or changed in any way. Open the registry editor by typing 'regedit' in the Start menu. Find the firewall keys (see Resources), right click each one and select 'Permissions.' Permissions should be allowed for the Local computer.
Unwanted Blocking
The most common problem with firewalls occurs when a program you need is blocked from the Internet. Users who upgrade to Windows XP or install Service Pack 2 will notice that some programs quit working. This is normal behavior, as it is the firewall's job to block unsolicited connections to your PC. Sometimes you have to open ports to fix the programs it believes are unsolicited. In Windows XP, Vista and Windows 7 a security alert should inform you that the program is being blocked. Click 'Unblock' to allow it. Do this once for each program.