I also encountered this problem when adding a new channel.
PHP version 5.4
More details for you:
Warning: Illegal string offset ‘attributes’ in \wp-content\plugins\automatic-youtube-video-posts\class\xml.php on line 377
Warning: Cannot modify header information – headers already sent by (output started at \wp-content\plugins\automatic-youtube-video-posts\class\xml.php:377) in \wp-includes\option.php on line 568
Warning: Cannot modify header information – headers already sent by (output started at \wp-content\plugins\automatic-youtube-video-posts\class\xml.php:377) in \wp-includes\option.php on line 569
