In the QCreate set up in the "Common module settings" it is possible to select three different Group modes: No groups, Visible groups, Separate groups.

If one sets Separate or Visible Groups, then a Groups menu appears when viewing the list of questions created by students (the Grading tab).

However, if one selects a specific group, i.e. one just wants to see questions made by students in a certain group, the following error message appears:

Not Found
The requested URL /moodle/mod/qcreate/grades.php was not found on this server.

Apache/1.3.33 Server at vle.c.fun.ac.jp Port 80

Note, the url for the list of questions in which this error appeared is:
http://vle.c.fun.ac.jp/moodle/mod/qcreate/edit.php?cmid=5362

and the url that gets the above error message is:
http://vle.c.fun.ac.jp/moodle/mod/qcreate/grades.php?id=5362&group=378

the correct url should be:
http://vle.c.fun.ac.jp/moodle/mod/qcreate/edit.php?cmid=5362&group=378