Authentication

[Moodle 2.7.17+ on LAMP Debian Jessy]

This site was stable since a major upgrade a couple of months ago. A couple of days ago the user synchronization stopped. The error message is copied here.

Obviously there is a prohibited username. The problem is, I do not get a decent error message, can't get the username in the output, and "potential coding error" is not very reassuring!

Is this known? Or, how can I find out the offending username? (The debug level has no effect on the output below.)

===
# /usr/bin/php /var/www/html/moodle/auth/ldap/cli/sync_users.php
Verbindung zum LDAP-Server aufbauen...Temporäre Tabelle tmp_extuser erstellen.
.........................................................................................
755 Datensätze von LDAP eingelesen
Keine Nutzerkonten zum Entfernen gefunden
Keine Nutzerkonten zum Reaktivieren gefunden
Keine Aktualisierung nötig
Nutzerkonten zum Hinzufügen: 11Database transaction aborted automatically in /var/www/html/moodle/auth/ldap/cli/sync_users.php
Default exception handler: Der Anmeldename enthält ungültige Zeichen Debug:
Error code: invalidusername
* line 49 of /user/lib.php: moodle_exception thrown
* line 954 of /auth/ldap/auth.php: call to user_create_user()
* line 63 of /auth/ldap/cli/sync_users.php: call to auth_plugin_ldap->sync_users()

!!! Der Anmeldename enthält ungültige Zeichen !!!
!!
Error code: invalidusername !!
!! Stack trace: * line 49 of /user/lib.php: moodle_exception thrown
* line 954 of /auth/ldap/auth.php: call to user_create_user()
* line 63 of /auth/ldap/cli/sync_users.php: call to auth_plugin_ldap->sync_users()
!! Potential coding error - existing temptables found when disposing database. Must be dropped!