The binding is wsHttpBinding with Message security. There is properly set large values for sendTmeOut and ReceiveTimeout, and large content length parameteres, bt i assume this is not where the problem lies, as there is no problem from other clients. Exercises with setting these values "wrong" has all given other reasonable exceptions in server log.
Seems as if something is corrupting the http request from this single client, and i have no idea what that may be...
Suggestions may be at great help.