I have upgraded from 1.95+ to 2.0RC2+. When a user with student role attempts a quiz, the following errors come up:

In the very beginning:

Error: Could not insert a new entry to the Moodle log
line 1686 of /lib/datalib.php: call to debugging()
line 77 of /mod/quiz/attempt.php: call to add_to_log()

In the final submission (Submit all and finish), the following messages come:

Notice: Undefined property: stdClass::$lastaccess in /xxxxxx/lib/messagelib.php on line 73

Notice: Undefined property: stdClass::$component in /xxxxxx/lib/messagelib.php on line 111

Notice: Undefined property: stdClass::$name in /xxxxxx/lib/messagelib.php on line 111

Coding error detected, it must be fixed by a programmer: Could not load preference message_provider___loggedoff. Does the component and name you supplied to message_send() match a row in message_provider? Message providers must appear in the database so users can configure how they will be notified when they receive messages.

Debug info: blah
Stack trace:
line 123 of /lib/messagelib.php: coding_exception thrown
line 1062 of /mod/quiz/locallib.php: call to message_send()
line 1155 of /mod/quiz/locallib.php: call to quiz_send_notification()
line 847 of /mod/quiz/attemptlib.php: call to quiz_send_notificartion_emails()
line 191 of /mod/quiz/processattempt.php: call to quiz_attempt->quiz_send_notification_emails()

Results of the attempt are not displayed.