If you didn't have "Debug" enabled before, you might not see any errors in your logs at all. You can still enable debug mode by adding these lines to your config.php file, before the "require_once(dirname(FILE) . '/lib/setup.php');" line:
$CFG->debug = E_ALL | E_STRICT;
$CFG->debugdisplay = 1;
ini_set('display_startup_errors', 1);
ini_set('display_errors', 1);
Saludos.
Iñaki.