They’ve given me the solution, and it works on my system.
1) Trash your FCP preferences (FCP Rescue 5 makes it more simple to do this). The important file to trash is the Obj Cache file, but the files work together, so trash all of them
2) Enable Caps Lock and start Final Cut
3) Immediately Quit FCP
4) Disable Caps Lock and start Final Cut again
Try adding a BCC4 filter. It it works, then set your FCP prefs again, and yuou should be Good To Go.
HTH.