Increase the size of session-ids.
function system_update_7057() {
$spec = array(
'description' => "A session ID. The value is generated by PHP's Session API.",
'type' => 'varchar',
'length' => 128,
'not null' => TRUE,
'default' => '',
);
db_change_field('sessions', 'sid', 'sid', $spec);
}