by Claire Browne.
I have solved my query.
I have removed from the 'Grade Column' which the program needed in order to get the correct user id for the column.
I love Moodle GIT Hub and Toritise SVN - Dif, always gets me out of sticky problem.
if (!$this->is_downloading()) {
// We have to call this column userid so we can use userid as a default sortable column.
$columns[] = 'userid';
$headers[] = get_string('edit');