Questionnaire (plugin)

I had the same error:
"If I want to view the questionnaire I get the above error, if I want to create new one I get this one:
Fatal error: Class 'questionnaire' not found in /home/moodle/mod/questionnaire/mod_form.php on line 19"

I fixed if by inserting this line at the start of questionnaire/mod_form.php:
require_once($CFG->dirroot.'/mod/questionnaire/locallib.php');