in calculated/questiontype.php line 1049
// Find a default unit:
if (!empty($questionid) && $unit = $DB->get_record('question_numerical_units',
array('question' => $questionid, 'multiplier' => 1.0)))

else

should be corrected to handle the more than one record with a multiplier value == 1,0.
see http://moodle.org/mod/forum/discuss.php?d=211619