Enrolment

I'm using moodle 1.9.9. I'm starting a new moodle platform for at first around 200 users that should work in a week. I've set up user authentication via an external database (mysql) and that works. I then tried to enrole users to courses via the same db and that doesn't!
First I've tried it with a view, then when I didn't get that to work, for testing I created a real table. In that (and also in the Enrolement setup) I then switched from username, coursename and rolename to userid, courseid and roleid... still no success...
I always had the 2 cronjobs auth/db/auth_db_sync_users.php and enrol/database/enrol_database_sync.php running and as said the first works. Both are aimed at the same database with the same db-user.

After having spend much time on that now I don't have another idea any more than to think that maybe 1.9.9 has a bug there? If anyone has a hint to what else I could try or maybe a way how to get to see the error log of enrol_database_sync.php (don't have access to the php.ini) I'd appreciate that! Thank you!