Error When Using WPMU Defender Options

Hey Guys:

I seem to be having some issues with a few of the Defender options. While I can use the Hardening and Scan Report features without any problems I am running into problems when I try to use the following features:

Audit Logging

I've gone into my wp-config.php file and changed the following line from
to match what I thought the plugins were suggesting....

but that didn't work so I changed it back. Can you please tell me where to go and what to change so I can use this feature?

Thank you,