I installed a Moen Sage toilet paper holder. The right cover that attaches to the wall hardware via a small screw is loose and no amount of tightening corrects the problem. What am I doing wrong?

It is likely that the the mounting post on the wall has pulled loose.

You will need to remove the paper holder and inspect themounting posts; loosen the set screws in the base of the posts to do this.

Try tightening the screws holding the mounting posts to the wall. If the screws are unable to hold tight you will need to replace the wall anchors if they have been used.

Remove the mounting posts and the wall anchors and replace with new wall anchor, preferably a toggle anchor designed for sheetrock if possible.

With the wall anchors in place attach the mounting posts and install the paper holder; tightening the set screws in at the base of the posts.

Installation instructions for your product can be found here:

http://www.moen.ca/shared/pdf/yb2208sp.pdf