It got me again, not escaping characters in my rss feed. I knew what was happening as soon as I saw the error this time though which helped, I still forgot to put the extra code in to start with though Also de-bugging was made harder because i.e. refused to admit that there was a new file there, instead insisting on complaining about the old error making me think it wasn't fixed after all.

$replace = array("&", "<", ">", "\"", "'");
$with = array("&amp;", "&lt;", "&gt;", "&quot;", "&apos;");
$aString = str_replace($replace, $with, $aString)