INSERT Statement Error, Not executing

Question

Trying to execute a SQL statement from data that is being input by the user from textboxes and once they click a button it should insert into the table, but is saying i have an error in the INSERT statement

This is the Button code when clicked:

 private void SaveBtn_Click(object sender, EventArgs e)
    {
        string Invoice = InvoiceNoTxt.Text;
        string Account = AccountTxt.Text;
        string dates = textBox1.Text;
        string TotalSells = TotalSellTxt.Text;
        string Vats = VatTxt.Text;
        string TotalCosts = TotalCostTxt.Text;

        if (EditChoice == 1)
        {
            //this is the SQL statement that updates the table
            Sql = String.Format("UPDATE InvoiceHeader " + "SET AccountCode = {0}," + "Day = '{1}'," + "TotalSell = {2}, " + "Vat = {3}, " + "TotalCost = {4}, "  + "WHERE InvoiceNo = {5};", Account, dates, TotalSells, Vats, TotalCosts, Invoice);
        }
        else
        {
            //this is the SQL statement that adds to the table in the database
            Sql = String.Format("INSERT INTO InvoiceHeader(AccountCode,Day,TotalSell,Vat,TotalCost) " + "VALUES " + "({0}," + "'{1}'," + "{2}," + "{3}," + "{4});", Account, dates, TotalSells, Vats, TotalCosts);
        }
        //this is calling the method that executes the SQL code
        La(Sql);
        //this reloads the data from the database with the new data in it
        LoadData();
        //this clears the data in the textfields and refreshs the panels to use again
        Back();
    }

this is the execute method to execute the sql:

 private void La(String Sql)
    {
        //this code in the method allows for the sql to execute from all the statements
        DbConn = new OleDbConnection(ConString);
        DbCmd = new OleDbCommand(Sql, DbConn);
        DbConn.Open();
        DbCmd.ExecuteNonQuery();
        DbConn.Close();
    }

Answer 1

It's probably the extra comma in your query text.

"UPDATE InvoiceHeader " + "SET AccountCode = {0}," + "Day = '{1}'," + "TotalSell = {2}, " + "Vat = {3}, " + "TotalCost = {4}, "  + "WHERE InvoiceNo = {5};"

It's easier to spot if you have your query text on multiple lines.

"UPDATE InvoiceHeader " + 
"SET AccountCode = {0}," +
"Day = '{1}'," + 
"TotalSell = {2}, " + 
"Vat = {3}, " + 
"TotalCost = {4}, " + // <-- here
"WHERE InvoiceNo = {5};"

Answer 2

The word 'Day' could be a system reserved word, try adding square brackets around it like such...

Sql = String.Format("INSERT INTO InvoiceHeader(AccountCode,[Day],TotalSell,Vat,TotalCost) " + "VALUES " + "({0}," + "'{1}'," + "{2}," + "{3}," + "{4});", Account, dates, TotalSells, Vats, TotalCosts);

Sql = String.Format("UPDATE InvoiceHeader " + "SET AccountCode = {0}," + "[Day] = '{1}'," + "TotalSell = {2}, " + "Vat = {3}, " + "TotalCost = {4}, "  + "WHERE InvoiceNo = {5};", Account, dates, TotalSells, Vats, TotalCosts, Invoice);