Websocket 'gatling.http.webSocket' was unexpectedly closed with status 4003 and message Invalid security key

I use Gatling 2.1.7 to test our websocket server

I copied the sample code and changed a little as follows

class WebsocketSimulation extends Simulation{
val httpConf = http
.baseURL(“https://xxx”)
.acceptHeader(“text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8”)
.doNotTrackHeader(“1”)
.acceptLanguageHeader(“en-US,en;q=0.5”)
.acceptEncodingHeader(“gzip, deflate”)
.userAgentHeader(“Gatling2”)
.wsBaseURL(“wss://xxx”)

val scn = scenario(“WebSocket”)
.exec(session => session.set(“sk”, “63ff221c1b1a0797afa5130cbbbaa8a6153cac830ff”))
.exec(ws(“Connect WS”).open("/websocket/message?securityKey=${sk}"))
.pause(1)
.exec(ws(“Close WS”).close)

setUp(scn.inject(atOnceUsers(1)).protocols(httpConf))
}


But when I ran gatling.sh, I got the following output:

2016-03-31 13:01:13                                           3s elapsed
---- WebSocket -----------------------------------------------------------------
[##########################################################################]100%
          waiting: 0      / active: 0      / done:1     
---- Requests ------------------------------------------------------------------
> Global                                                   (OK=1      KO=1     )
> Connect WS                                               (OK=1      KO=0     )
> Close WS                                                 (OK=0      KO=1     )
---- Errors --------------------------------------------------------------------
> Websocket 'gatling.http.webSocket' was unexpectedly closed wit      1 (100.0%)
h status 4003 and message Invalid security key.

What happened? It seems that the websocket connection isn't closed although I invoked *ws("Close WS").close* method.

Can anyone give some advice?
Thanks in advance

Sorry, 4003 is the status code returned from the server indicating security key is invalid