Root Element Missing

All

I have a web service that has been working fine until yesterday evening, I don't remember making any changes, but for some reason since yesterday evening I am getting the message "WSE910: An error happened during the processing of a response message, and you can find the error in the inner exception. You can also find the response message in the Response property." with inner exception as "Root Element Missing". I checked the xml file generated and can't find anything mistakes in it. Appreciate your help

Sri

Here is my web service SOAP
POST /dactrak/services/actraktransporter.asmx HTTP/1.1
Host: sta12
Content-Type: text/xml; charset=utf-8
Content-Length: length
SOAPAction: "http://www.dacms.com/actrak/transporter/1_0/GetInspectorAssignmentsDiff"

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi=&qu ...