Calling WCF service with jquery and parameters synchronously

Question

Hi, I am calling a .NET WCF service from Ajax like this:

result = $.ajax({
    type: "POST",
    // async: false,
    contentType: "application/json; charset=utf-8",
    url: BaseUrl + "Services/YucataService.svc/SetGameStatusSecure",
    data: "{'gameID':'" + gameID + "','pid':'" + pid + "','status':'" + newStatus + "','origStatus':'" + oldStatus + "'}",
    dataType: "json",
    timeout: 20000
});

The server part looks like this:

[OperationContract]
public void SetGameStatusSecure(int gameID, int pid, string status, string origStatus)
{
   ... magic stuff happens
}

It works well.

Now, I would like to call the service synchronously. The only change I do is to add "async: false". The call return with status 500 (=internal server error).

Do I have to configure the WCF service differently to allow sync calls?

Before I switched to WCF I used an .asmx service to call synchronously and I didn't have any issues.

Any ideas?