Input string was not in a correct format.Couldn't store <emp8> in id Column. Expected type is Int32

protected void Button1_Click(object sender, EventArgs e)
    {
        c.cmd.CommandText = "select * from newuser";
        c.adp.Fill(c.ds, "vT");
        c.dr = c.ds.Tables["vT"].NewRow();
        c.dr["id"] =c.auto_id("emp",c.ds.Tables["vT"].Rows.Count);//i am getting error here
        c.dr["username"] = txtusername.Text;
        c.dr["first_name"] = txtfname.Text;
        c.dr["password"] = passtxt.Text;
        c.dr["image"] = "~//new_user_image/" + ImgUpload.FileName;
        c.dr["phone"] = txtphone.Text;
        c.dr["email"] = emailtxt.Text;
        c.dr["status"] = "false";
        c.dr["login_status"] = "false";
        c.ds.Tables["vT"].Rows.Add(c.dr);
        c.cb = new SqlCommandBuilder(c.adp);
        c.adp.Update(c.ds.Tables["vT"]);
        ImgUpload.SaveAs(Server.MapPath("~//new_user_image/" + ImgUpload.FileName));
        Response.Redirect("success_signup.aspx");

    } 
 
i am getting error please tell me how to resolve it 

himanshu