Listbox.selectedIndex returns value of -1

I am creating a delete button for a project I am working on, but when I try to delete the selected value from a database it gives me an error of index out of range.  And the value return is -1.

The code below is what I am working on:

private void btnDeleteBook_Click(object sender, EventArgs e)
    {
        string sql;
        if (lstBooks.SelectedIndex == -1)
        {
            ShowMessage("Please select a item to delete.");
            return;
        }
        clsBooks tempRecord = (clsBooks)mBooks[lstBooks.SelectedIndex - 2];
        int id = tempRecord.BookID;
        if (MessageBox.Show("Please review the record details and click OK to confirm your delete request.", "Confirm Delete", MessageBoxButtons.OKCancel) !=
            DialogResult.OK)
        {
            ShowMessage("Delete request cancled.");
            return;
        }

        sql = "DELETE FROM EBOOK WHERE BookID = " + clsSQL.ToSql(id) + ";";

        try
        {
            openDatabaseConnection();
            mDB.Open();
            OleDbCommand cmd;
            cmd = new OleDbCommand(sql, mDB);
            cmd.ExecuteNonQuery();
            ShowMessage("The record has been deleted from the Ebook Table.");
        }
        catch (Exception ex)
        {
            ShowMessage("There was an unexpected problem deleting the records: " + ex.Message);
        }
        finally
        {
            closeDatabaseConnection();
        }

        LoadDBTable("SELECT * FROM EBOOK Order BY BookID;");
        showBooks();
    }