无法在多线程调用C＃MVC中下载文件

Question

public ActionResult Download(string fileGuid, string fileName)
{          
     var File = MyMethod(fileGuid, fileName);
return File;
}

public virtual ActionResult MyMethod(string fileGuid, string fileName)
{
    //Gets Download data 
    Response.AppendHeader("Content-Disposition", "attachment"))
    //refers filelocation which the file
    return File( filelocation, contentType);/
}

如果将方法调用置于线程中，则无法下载文件。我收到以下错误：

  

{“值不在预期范围内。”}在Response.AppendHeader处