Sesskey value needs to be set for download link in /mod/assignment/type/peerreview/assignment.class.php at line 262. /mod/assignment/type/peerreview/assignment.class.php line 262 echo '<a onclick="setTimeout(\'document.getElementById(\\\'continueButton\\\').disabled=false;\',3000);return true;" href="'.$CFG->wwwroot.'/mod/assignment/type/peerreview/'.self::DOWNLOAD_PEERREVIEW_FILE.'/'.self::FILE_PREFIX.($numberOfReviewsCompleted+1).'.'.$this->assignment->fileextension.'?a='.$this->assignment->id.'&id='.$this->cm->id.'&sesskey='.sesskey().'"><img class="icon" src="'.$CFG->pixpath.'/f/'.mimeinfo('icon', 'blah.'.$this->assignment->fileextension).'" alt="'.get_string('lostfile','assignment_peerreview').'" />'.get_string('lostfile','assignment_peerreview').'</a>';