In /moodle/enrol/database/enrol.php:

After setting ADODB_FETCH_ASSOC per MDL-7443, the $enroldb's reference of $rs->fields[0] is undefined (at least for the Informix driver), and database enrollment fails. Reference by association works as below.

Changed /moodle/enrol/database/enrol.php 1.27, line 87:
< $courselist[] = $rs->fields[0];
—
> $courselist[] = $rs->Fields($CFG->enrol_remotecoursefield);