Saving related entry in a Matrix block programmaticially
Possibly a duplicate of this one here but hey, here is where I think you are going wrong:

Change this part:

$block-&gt;getContent()-&gt;setAttributes(array(
  'contentRss' =&gt; array($entry-&gt;id)
));


To this:

$block-&gt;getContent()-&gt;contentRss = array($entry-&gt;id);