Linq to SQL InsertOnSubmit error

I cannot figure out why I am getting this error, please help. The errors occure on line 12

 1 protected void btnInsert_Click(object sender, EventArgs e)
2 {
3 //if(txtName.Text != "" && txtPosition.Text != "")
4 {
5
6 AlternaDB.MarketingDataContext db = new AlternaDB.MarketingDataContext();
7
8 Distributor tbl = new Distributor();
9 //tbl.AccountType = dpAccountType.SelectedValue;
10
11 tbl.CompanyName = txtCompanyName.Text;
12 db.Distributors.InsertOnSubmit(tbl);
...