Hello Senthur !
The shown error means that this line in inc/classes/BxDolTranscoder.php:
$o = self::getObjectInstance($r['transcoder_object']);
gives the wrong object. You may try to execute the following query in your UNA database (you may backup this table before):
DELETE * FROM `sys_transcoder_queue` WHERE `status` = 'processing';
and try to upload the new video again. Then check the new result.