CRM 2013 plugin on Export message?

I have registered a simple plugin against the Export message. However, I am not seeing my plugin execute. Is is set as pre-validation plugin. The plugin itself just throws an error. Since it's synchronous, it should just popup on-screen.

Ideally, I was looking to see the error popup when attempting an export. So far, nothing. I tried this on the "ExportAll" message as well. 

Any thoughts?

Ultimately, I'm trying to restrict certain entity exports and not others.