When you have list of assignments (http://yourmoodle.org/mod/assignment/submissions.php) with "filter" displaying only assignments requiring grading and there is no assignment requiring grading (all assignments were already graded), then view of assignments is corrupted. Even worse you can't view any assignment anymore. It is due to small bug in Moodle. I'm attaching patch for this bug (I edited this diff file and it is hopefully correct diff file).