There was an error in Security & Privacy preferences I head on to Security &amp; Privacy on Filevault and try to encrypt my disk. When I click the Turn On Filevault I get the error.

When going through the syslog I see this:

Dec  3 00:09:48 --- last message repeated 7 times ---
Dec  3 00:09:48 MacBook-Pro com.apple.xpc.launchd[1] (com.apple.preference.security.remoteservice[30942]): Service exited due to signal: Illegal instruction: 4 sent by exc handler[0]
I saw the same error, and I was able to solve this via a reboot--hope that helps!

I can't say for 100% certainty, but I believe I still had some pending updates that had not yet installed: I remember when I was scanning the output of syslog that I also saw some references to a class being implemented in two different files, so I thought that could have been an artefact of an update that had not yet completed. Again, I admit to being a little unsure as to the exact cause of the problem and solution, but this was what worked for me.