So was Guardian working but then after upgrading to Core Update 159 it stopped or are you trying to get it running and it is failing to do so.
I am on Core Update 159 and I just installed Guardian, checked the Enable Guardian box and then pressed save and Guardian started with no problems.
Run the following command to see what the logs say
less /var/log/messages | grep guardian
There should be some messages in there indicating what is causing it to not start
Is this an Internal Server Error message. If yes then you should be able to find some indication of what the error is by looking at the following log. The best idea is to click to access the url logs, get the error message and then go to the console and access the above log. The appropriate error messages will be near the end of the log.