'topratings' is a parameter passed to an URL when you want to display the "Top rated pictures" page. This parameter has been renamed to 'toprated' in the 0.9.13 release of phpGraphy.
If you haven't updated your templates, or if you've static links pointing to this page (from .welcome files etc.), you'll get this error message.
To correct the problem, simply change your links to use the new parameter.
ie:
<a href="http://somesite.com/phpgraphy/index.php?topratings=1">
should now be
<a href="http://somesite.com/phpgraphy/index.php?toprated=1">