PHP Fatal error when trying to synchronize users

Environment:
Ubuntu 10.04
PHP 5.3.2
Mysql 5.1.41
Drupal 6.24
CiviCRM 4.1b3

I have enabled the following modules: civicrm, civicrm_cck, civicrm_group_roles, civicrm_member_roles

When I go to /civicrm/admin/synchUser?reset=1 and then click OK on the displayed page I get a white screen of death (error 500)

The apache error log contains the following message:

[Thu Feb 02 20:53:32 2012] [error] [client 173.62.56.223] PHP Fatal error: Call to undefined method mysqli_result::fetchAssoc() in /XXXXXXXXX/sites/all/modules/civicrm/CRM/Core/BAO/CMSUser.php on line 69, referer: http://XXXXXXXXXXXXXX/civicrm/admin/synchUser?reset=1