unable to find DropDown Control in gridview in RowUpating event

   protected void GridViewDepartment_RowUpdating(object sender, GridViewUpdateEventArgs e)  
    {                       getConnection = connection.SetConnection();
                       GridView GridViewDepartment = (GridView)sender;
                       GridViewDepartment.EditIndex = e.RowIndex; // Update Index You Want to edit
                       GridViewDepartment.DataSource = departmentTable; // ReBind the GridView
                       GridViewDepartment.DataBind();
                       int DepartmentID = (int)GridViewDepartment.DataKeys[e.RowIndex].Value;
                       DropDownList ddlManager = ((DropDownList)GridViewDepartment.Rows[e.RowIndex].FindControl("ddlDepartManager"));
                     string AssignNewManagr = ddlManager.SelectedItem.Text.ToString();
                      Response.Write(AssignNewManagr);
                      string AssignNewActive = ((DropDownList)GridViewDepartment.Rows[e.RowIndex].FindControl("DropDownListActive")).SelectedItem.ToString();
                     Response.Write(AssignNewActive);
                     string SPUPDateDepartment = "SPModifyDepartment";
                     SqlCommand UPDateCommnad = new SqlCommand(SPUPDateDepartment, getConnection);
                     UPDateCommnad.CommandType = CommandType.StoredProcedure;
                     UPDateCommnad.Parameters.AddWithValue("@DepartmentId", DepartmentID);
                     UPDateCommnad.Parameters.AddWithValue("@DepartmentManager", AssignNewManagr);
                     UPDateCommnad.Parameters.AddWithValue("@Active", AssignNewActive);
                     UPDateCommnad.ExecuteNonQuery();
                     GridViewDepartment.EditIndex = -1;
                     GetDepartmentList();    }