If the server/application being load tested does not include the Content-Type header in its response it can cause the load test to fault with:

[08/11 22:28:18,Telerik.TestStudio.Load.Agent.exe(6852:14),Error] OutstandingRequest.Run() : EXCEPTION! (see below)
     Situation: Exception during HTTP Request, url [https://ptinformrmsweba.tritech.local/sts/issue/wsfed?wa=wsignin1.0&wtrealm=https%3a%2f%2fptinformrmsweba.tritech.local%2finformrms%2f&wctx=rm%3d0%26id%3dpassive%26ru%3d%252fInformRMS%252f&wct=2014-08-11T16%3a06%3a59Z]
     Outer Exception Type: System.ArgumentNullException
     Message: Value cannot be null.
          Parameter name: contentType
     HRESULT: 0x80004003 (Official ID (if app.) = E_POINTER, Error Bit = FAILED, Facility = FACILITY_NULL, Code = 16387)
     Call Stack:
          at System.Net.Mime.ContentType..ctor(String contentType)
          at Telerik.TestStudio.Load.Http.OutstandingRequest.TransformContentForBindings(String strContentType, HttpResponseBuilder responseBuilder)
          at Telerik.TestStudio.Load.Http.OutstandingRequest.<Run>d__0.MoveNext()