A user uploads a PDF assignment submission. The instructor annotates it. When the user tries to view the annotated PDF by clicking on the "View annotated PDF..." button.
They are presented with the following error in a pop up window:
Sorry, but you do not currently have permissions to do that (Grade assignment)
It looks like it is hitting the following piece of code(around line 133 in mod/assign/feedback/editpdf/ajax.php):