halleluuja

I remember I used to have similar problem once. It happened when no themes were activated.

This line also needs to be changed:

<param name="allowFullScreen" <a href="https://www.studentnews.ie/topic/value">value</a>="true"></param>

This is correct:

<param name="allowFullScreen" value="true"></param>

I think I finally detected the bug:

<param name="movie" value="https://www.<a href="https://www.studentnews.ie/topic/youtube">youtube</a>.com/v/6AR51Jo2Tmw?version=3&hl=en_US&rel=0"></param>

Change this line to this:

<param name="movie" value="https://www.youtube.com/v/6AR51Jo2Tmw?version=3&hl=en_US&rel=0"></param>

Could you upload the modified page? I still have strong feeling that answer must be somewhere in the HTML.

Maybe this section in the page source has something to to with it:

<!-- AddThis Button BEGIN -->
<div class="addthis_toolbox addthis_default_style ">
<a class="addthis_button_facebook_like" fb:like:layout="button_count"></a>
<a class="addthis_button_tweet"></a>
<a class="addthis_button_google_plusone" g:plusone:size="medium"></a>
<a class="addthis_button_email">&nbsp;
<a class="addthis_button_print">&nbsp;
<a class="addthis_counter addthis_pill_style"></a>
</div>
<script type="text/javascript" src="https://s7.addthis.com/js/250/addthis_widget.js#pubid=xa-4f145ae36adbb0be"></script>
<!-- AddThis Button END -->

This section has two missing tags and this may cause conflict with that line:

<a href="https://www.studentnews.ie/topic/youtube">youtube</a>

SOLVED!

All I needed to do was simply visit the Settings > Permalinks page on Admin area. That caused the rewrite rules to be flushed — and my plugin became to work like a charm.