Having Error trying to insert records

Hi am having error trying to insert records to database and i dont really know were the problem is coming from
Here is the code i used:
protected void btnSubmit_Click(object sender, EventArgs e) { Connection(); query = "Sells"; //Stored Procedure name SqlCommand com = new SqlCommand(query, con); //creating SqlCommand object com.CommandType = CommandType.StoredProcedure; //here we declaring command type as stored Procedure //* adding paramerters to SqlCommand below *\ com.Parameters.AddWithValue("@Date", txtSalesDate.Text.ToString()); //date com.Parameters.AddWithValue("@Customer_Name", txtCustomer_Name.Text.ToString()); com.Parameters.AddWithValue("@Staff ", txtAdminstratorsID.Text.ToString()); //Name of rep com.Parameters.AddWithValue("@Delivery ", txtDeliveryAddress.Text.ToString()); //Add ...