When are you getting this error? While calling or is it appearing in server.log while starting or reloading… Are you sure the WSD Consumer is present in the same IS?
I am getting this error while calling webService, yes WSD is present in same IS.
It is not a contineous behaviour, only for some ws call (say 1 out of 300) it is failing.
As per my observation this failure occurs only when I deploy any new patch (which is havinq code changes in same package in which WSD resides). I am very sure webservice call happens after deployment process completed.