Creating new instance

Hi, I am very new to C#, and have an error on click of the save button. I have created a simple WPF application using Visual Studio, and have a SQL databased linked in. I have 3 buttons on the page, one to go to the next record, one to nacigate to the previous, and one to save.

CollectionViewSource tblOrdersViewSource = null;
PO2DataSet PO2DataSet = null;
PO2DataSetTableAdapters.TblOrdersTableAdapter pO2DataSetTblOrdersTableAdapter;


private void Window_Loaded(object sender, RoutedEventArgs e)
{

WPFPurchaseOrders.PO2DataSet pO2DataSet = ((WPFPurchaseOrders.PO2DataSet)(this.FindResource( "pO2DataSet")));
// Load data into the table TblOrders. You can modify this code as needed.
pO2DataSetTblOrdersTableAdapter = new WPFPurchaseOrders.PO2DataSetTableAdapters.TblOrder sTableAdapter();
pO2DataSetTblOrdersTableAdapter.Fill(pO2DataSet.Tb lOrders);
tblOrdersViewSource = ((System.Windows.Data.CollectionViewSource)(this.F indResource("tblOrdersViewSource")));
tblOrdersViewSource.View.MoveCurrentToFirst();
// Load data into the table TblItem. You can modify this code as needed.
WPFPurchaseOrders.PO2DataSetTableAdapters.TblItemT ableAdapter pO2DataSetTblItemTableAdapter = new WPFPurchaseOrders.PO2DataSetTableAdapters.TblItemT ableAdapter();
pO2DataSetTblItemTableAdapter.Fill(pO2DataSet.TblI tem);
System.Windows.Data.CollectionViewSource tblOrdersTblItemViewSource = ((System.Windows.Data.CollectionViewSource)(this.F indResource("tblOrdersTblItemViewSource")));
tblOrdersTblItemViewSource.View.MoveCurrentToFirst ();
}

private void previousButton_Click(object sender, RoutedEventArgs e)
{
tblOrdersViewSource.View.MoveCurrentToPrevious();
}

private void nextButton_Click(object sender, RoutedEventArgs e)
{
tblOrdersViewSource.View.MoveCurrentToNext();
}

private void saveButton_Click(object sender, RoutedEventArgs e)
{
if (pO2DataSetTblOrdersTableAdapter.Update PO2DataSet.TblOrders) > 0)
{
MessageBox.Show("Changes were saved");
}
else
{
MessageBox.Show("No changes were made or saved");
}
}

The error is on the first line of the if statement. The error message 'NullReferenceException was unhandled'. When reading the troubleshooting tips it mentions creating a instance for the class, but I thought this was already done at the top of the code?

Any suggestions/explinations is much appriciated.

Many thanks.