A query that fails returns the child node <error>, for example:

<result

  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

  xmlns:xsd="http://www.w3.org/2001/XMLSchema"

  xmlns="http://www.teradp.com/schemas/GN4/1/Results.xsd">

 <error

  code="1903"

  name="SearchMissingParameter"

  message="Search conditions: missing parameter 'param' (ERR1903)"/>