Enable User Audit - Where did I go wrong?

I had some items in my NPM go missing last night, and although I have a pretty good idea where they went, I want to look at the logs to see who did it.  Well, When I follow the instructions of adatole suggestion about filtering results in Message Center, I get nothing:

How do I see the audit trail?

Also, when I go to Reports and run the "Last 100 Audit Events" report, it comes back blank.  Any suggestions on where to look and see where I went wrong? 

Thanks,
niterave