Usando moodle 1.9.3 (Build: 20081015)
Para poder ver los mensajes de error que moodle muestra hay que entrar como administrador.
Dentro del panel de Administración del Sitio seleccionar Servidor / Depurando
En “Depurar mensajes” (debug) Seleccionar “DESARROLLADOR: mensajes extra de depuración Moodle para desarrolladores”.
Documentación sobre el tema en:
http://docs.moodle.org/en/Debugging#How_to_turn_on_debugging
How to turn on debugging
Go into the admin screens, and look under Administration > Server > Debugging (In Moodle 2.0 it is Site administration ▶ Development ▶ Debugging). Set the…
* Debug messages to ALL, and
* Display debug messages to Yes.
(You must do both). There is rarely any advantage in going to Developer level, unless you are a developer, in which case it is strongly recommended.
Once you have got the error message, and copied and pasted it somewhere, you are recommended to turn debugging back off again.
.