SOAP Exception

Hi All,
we are trying to post data to a webservice from webmethods.we are occasionally getting the following error.
“SOAPException: [ISS.0088.9136] A WattEvaluationException was thrown by the XQL Query engine”
Can any one throw light on this?what should be done to resolve this error.
Our IS version is 6.1.

Thanks,
Santosh