The update froze with "Error writing to database" when trying to upgrade from Moodle 1.9.10+ (Build: 20101103) to Moodle 2.0 (weekly release 26 of dec 2010). Database encoding is utf-8. Similar issues is described in => http://tracker.moodle.org/browse/MDL-22503 but the patch from is from the may 2010 and is not working actual release.

The Debug info is pointing out the duplicate of a 'teacher' role which I've named "Manager":

Debug info:
Duplicate entry 'Manager' for key 'mdl_role_nam_uix'

UPDATE mdl_role SET name = ?,shortname = ?,description = ?,sortorder = ?,archetype = ? WHERE id=?

[array (

0 => 'Manager',

1 => 'manager',

2 => 'Managers can access course and modify them, they usually do not participate in courses.',

3 => '0',

4 => 'manager',

5 => '1',

)]

Stack trace:

line 394 of /lib/dml/moodle_database.php: dml_write_exception thrown

line 959 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()

line 991 of /lib/dml/mysqli_native_moodle_database.php: call to mysqli_native_moodle_database->update_record_raw()

line 2872 of /lib/db/upgrade.php: call to mysqli_native_moodle_database->update_record()

line 1309 of /lib/upgradelib.php: call to xmldb_main_upgrade()

line 252 of /admin/index.php: call to upgrade_core()