This error appeared on every individual post after adding facebook comments.
What was causing this was the facebook comments appearing twice in my xml.
As well as...
And this was causing a conflict.
So I removed the fb:comments and -problem solved.
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What was causing this was the facebook comments appearing twice in my xml.
<fb:comments colorscheme='light' expr:href='data:post.canonicalUrl' expr:title='data:post.title' expr:xid='data:post.id' width='600'/>
As well as...
<div class='fb-comments' data-type='button' expr:href='data:post.canonicalUrl' expr:title='data:post.title' expr:xid='data:post.id' locale='el_GR' width='600'/>
And this was causing a conflict.
So I removed the fb:comments and -problem solved.