Check your config file as something is not conforming to XML.  If you edit it in notepad and save it that is fine, but open it with an XML viewer like IE and it will probably give you an error (or it will look all messed up).  ORFilter uses XML parsing, so your config file has to conform to XML standards.  Having a < or > symbol in your rules causes the XML parsing to fail.  Something in the config file is not allowing ORfilter complete it parsing.

An example is if you are trying to find < this less than symbol in one of your rules then your config file or rule is incorrect.  FYI to look for a < you need to replace it in the config file with &lt;   the > is &gt;