There are many reasons for this exception. We  also got this same exception coiple of times and every time we debug we got different reasons.
Major one is when ever the siebel server is down,
Next when ever you are using a incorrect business component or the field doesn’t get the dersired values for the corresponding business component.
The exception is raised in siebeel, so debugging fromt eh siebel side whill give you the solution. For safe side try to apply siebel patches availble on the advantage site.
#Adapters-and-E-Standards#Integration-Server-and-ESB#webMethods