title: Error headers: ap_headers_output_filter() after putting cache header in htaccess file
body: <p>Receiving error: [debug] mod_headers.c(663): headers: ap_headers_output_filter()</p>
  
  <p>after I included this within the htaccess file:</p>
  
  <pre><code># 6 DAYS
  &lt;FilesMatch "\.(ico|pdf|flv|jpg|jpeg|png|gif|js|css|swf)$"&gt;
  Header set Cache-Control "max-age=518400, public"
  &lt;/FilesMatch&gt;
  
  # 2 DAYS
  &lt;FilesMatch "\.(xml|txt)$"&gt;
  Header set Cache-Control "max-age=172800, public, must-revalidate"
  &lt;/FilesMatch&gt;
  
  # 2 HOURS
  &lt;FilesMatch "\.(html|htm)$"&gt;
  Header set Cache-Control "max-age=7200, must-revalidate"
  &lt;/FilesMatch&gt;
  </code></pre>
  
  <p>Any help is appreciated as to what I could do to fix this?</p>