Parameterized Query '(@cid int)Select clogo from tbl_company1 where cid=@cid' expects parameter @cid, which was not supplied. Statement(s) could not be prepared.

Parameterized Query '(@cid int)Select clogo from tbl_company1 where cid=@cid' expects parameter @cid, which was not supplied.
Statement(s) could not be prepared.

public void ProcessRequest (HttpContext context)
   {
      // SqlConnection cn = new SqlConnection(ConfigurationManager.ConnectionStrings["Connection"].ConnectionString);
       SqlConnection cn = new SqlConnection(ConfigurationManager.AppSettings["constring"].ToString());
       cn.Open();

     string sql = "Select clogo from tbl_company1 where cid=@cid";
       SqlCommand cmd = new SqlCommand(sql, cn);
      cmd.Parameters.Add("@cid", SqlDbType.Int).Value = context.Request.QueryString["cid"];
      cmd.Prepare();
       SqlDataReader dr = cmd.ExecuteReader();
    //  dr.Read();
      if (dr.Read())
      {
          //context.Response.ContentType = dr["imagename"].ToString();
          context.Response.BinaryWrite((byte[])dr["clogo"]);
      }
      dr.Close();
     cn.Close();

  }