Error al leer en la base de datos

Hola que tal:

El motivo del post es para ver si me pueden ayudar porque al migrar moodle del 1.9 al 2.5 sale el error que a continuación pondré cuando se ejecuta el cron:

Server Time: Tue, 28 May 2013 15:06:34 +0000


 Created missing context instances
Cleaned up stale user sessions
Running auth crons if required...
... started 15:06:34. Current memory use 17.9MB.
Running enrol crons if required...
Running cron for enrol_manual...
... started 15:06:34. Current memory use 18.7MB.
Verifying manual enrolment expiration...
...manual enrolment updates finished.
manual enrolment expiry notifications were already sent today at Tuesday, 28 de May de 2013, 08:36.
Running cron for enrol_self...
... started 15:06:34. Current memory use 18.8MB.
Verifying self-enrolments...
...user self-enrolment updates finished.
No expired enrol_self enrolments detected
self enrolment expiry notifications were already sent today at Tuesday, 28 de May de 2013, 08:36.
Starting activity modules
Processing module function assignment_cron ...... started 15:06:34. Current memory use 24.7MB.
... used 2 dbqueries
... used 0.01444411277771 seconds
done.
Processing module function chat_cron ...... started 15:06:34. Current memory use 26.2MB.
... used 5 dbqueries
... used 0.0042660236358643 seconds
done.
Processing module function forum_cron ...... started 15:06:34. Current memory use 28MB.
Starting digest processing...
Cleaned old digest records
... used 3 dbqueries
... used 0.0044980049133301 seconds
done.
Processing module function quiz_cron ...... started 15:06:34. Current memory use 28.4MB.

  Looking for quiz overdue quiz attempts...
  Considered 0 attempts in 0 quizzes.
Starting quiz reports
Finished quiz reports
... used 2 dbqueries
... used 0.037900924682617 seconds
done.
Processing module function scorm_cron ...... started 15:06:34. Current memory use 32.6MB.
... used 1 dbqueries
... used 0.0075671672821045 seconds
done.
Processing module function workshop_cron ...... started 15:06:34. Current memory use 33.4MB.
 processing workshop subplugins ...
Starting workshop allocation methods
Processing cron function for workshopallocation_scheduled...
... started 15:06:34. Current memory use 34.5MB.
... no workshops awaiting scheduled allocation. done. (1 dbqueries, 0 seconds)
Finished workshop allocation methods
!!! Error al leer de la base de datos !!

espero me puedan ayudar gracias.