Call Method from Master Page

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C#3.0

C#

My previous post on this topic have been answered successfully.However when i access the method in the master page a error pops up saying object reference not set to an instance of an object..Heres the code

public bool CheckErrors()
   {
       Page.Validate(valSummary.ValidationGroup);//error is in this line
       if (!Page.IsValid)
       {
           update.Update();
           modalPopupEx.Show();
           return false;
       }
       return true;
   }

my call to the method from the other form is

protected void ImageButton2_Click(object sender, ImageClickEventArgs e)
    {
        SiteMaster master = (SiteMaster)this.Master;
        if (master.CheckErrors())
        {
            GridView2.Visible = false;
            gvsearch.Visible = true;

            string search = txtsearch.Text.ToString();
            gvsearch.DataSource = DataBase2.myProcedureName(search);
            gvsearch.DataBind();
        }
    }

Thanks