This is caused by an incorrect method call as part of the calculated grade support that has been added to the entry state field in 2.6.3.

mod/dataform/field/entrystate/ajax.php, line 68

$df->update_calculated_grade($entry->userid, "##\d*:$field->name##");

is missing a character. The called method name should be 'update_calculated_grades' (plural grades):

$df->update_calculated_grades($entry->userid, "##\d*:$field->name##");