It appears tha moderators cannot lock or unlock threads.

I think the error is in "posting.inc.php"

line 1465
// if user is authorized to lock:
if(isset(...) && ... || isset($_GET['lock']) && ...)

Should be
if(isset(...) && ... || isset($_GET['lock_thread']) && ...)

similarly a little bit below
// if user is authorized to lock:
if(isset(...) && ... || isset($_GET['lock']) && ...)

Should be
if(isset(...) && ... || isset($_GET['unlock_thread']) && ...)

Otto