You are most welcome

Variable <MENTALRAY_DIR> is supposed to point to the directory where mental ray is installed.

Make a backup copy of the file and change all instances of:
+ LOCALE:en_US mayatomr 3.13.1.8...

Can you post the content of C:\Program Files\Common Files\Autodesk Shared\Modules\Maya\2016\mentalray.mod

It is a text file so you can open it with notepad.

You need the plugin.

You'll have to download and install the mental ray plugin for Maya 2016 SP1.
http://knowledge.autodesk.com/support/maya/downloads/caas/downloads/content/autodesk-maya-2016-service-pack-1.html