A quick fix for 0.6.12
See Trac report for more details.
Just follow the INSTALL.txt instructions included in the package.
plugins/search/search.php system/core/users/users.auth.inc.php system/core/users/users.register.inc.php system/core/users/users.profile.inc.php system/core/plug/plug.inc.php system/core/list/list.inc.php system/functions.php