this error display("this causes Two binding source...")

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C#

ADO.NET

C#4.0

hii,everyone

when click on display button more than one click this error display("this causes Two binding in the collection to bind to the same property parameter name: binding")

this is my code:

da.SelectCommand = new SqlCommand("select * from student ",cs);

DataTable dt = new DataTable();
        ds.Clear();
        da.Fill(ds);

        dt=ds.Tables[0];
        dataGridView1.DataSource = ds.Tables[0];

  tblnamesbs.DataSource = dt;
 this.textBox1.DataBindings.Add(Text,this.tblnamesbs,firstname,true);//error
 this.textBox2.DataBindings.Add(Text,this.tblnamesbs,lastname,true);