Yes, it is XML messages. The messages consist of some standard data and a few binary file attachments. The same XML message sent with small size attachments works fine, but large size attachments gives this error. However, this is only related to one client location, and not the other locations, so I think it must be some infrastructure causing the problems, like something wrapping up the http request, or truncating it, but I am still totally out of ideas of what may cause this.