You must boot into the Recovery OS. You do this by restarting your machine, and holding
COMMAND + R until the Apple logo appears.
Then select Terminal from the Utilities menu. It looks like this:
In the window that opens, type
csrutil clear and press return.
This clears existing configuration of System Integrity Protection to default state which is "enabled".
reboot and press return to restart your machine.
More information about TotalFinder and System Integrity Protection.