<p>I had the same issue, indeed changing renderd.conf setting of mapnik_plugin set to the output of <code>mapnik-config --input-plugins</code> got rid of the error message.</p>

<p style="font-size:small;-webkit-text-size-adjust:none;color:#666;">—<br>Reply to this email directly or <a href="https://github.com/openstreetmap/mod_tile/issues/2#issuecomment-153865064">view it on GitHub</a>.<img alt="" height="1" src="https://github.com/notifications/beacon/AD2-7oLzWCybFDEHE7CXhZXlWyRcS8nDks5pCmp3gaJpZM4Ag7mC.gif" width="1" /></p>
<div itemscope itemtype="http://schema.org/EmailMessage">
<div itemprop="action" itemscope itemtype="http://schema.org/ViewAction">
  <link itemprop="url" href="https://github.com/openstreetmap/mod_tile/issues/2#issuecomment-153865064"></link>
  <meta itemprop="name" content="View Issue"></meta>
</div>
<meta itemprop="description" content="View this Issue on GitHub"></meta>
</div>