gettiing error:No mapping exists from object type System.Web.UI.WebControls.GridViewRow to a known managed provider native type.

here is my code:
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click Dim constr As String = ConfigurationManager.ConnectionStrings("oapConnectionString").ConnectionString Using con As New SqlConnection(constr) Dim sumQty As Integer = 0 For Each row As GridViewRow In GridView1.Rows Dim quantity = Convert.ToInt32(DirectCast(row.FindControl("TextBox1"), TextBox).Text) sumQty += quantity Next If sumQty < 100 Then Using cmd As New SqlCommand("INSERT INTO [OAP].[dbo].[Beneficiary_max_limit]([District_Code],[Block_Code],[District_max_value])VALUES (@District_Code, @Block_Code, @District_max_value)") cmd.CommandType = CommandType.Text cmd.Connection = con con.Open() cmd. ...