Scrolling within datagrid

I have a datagrid with its DataSource set to a dataset.

The first time the user clicks on the button "show" 25 records are read.

Now I need the following functionality:
If the user scrolls down and the last record is reached, the next 25 records should be read.

This is how I tried to do it:

VB Code:

Private Sub grdDataGrid_Scroll(...) Handles grdDataGrid.Scroll
    Dim intShowAnzahl As Integer
    Try
        intShowAnzahl = dgcTopLeftVisibleCell.RowNumber + Me.grdDataGrid.VisibleRowCount
        If intShowAnzahl = intSatzAnzahl Then
            DataGridLoadNext()
        End If
    Catch ex As Exception
        ErrorMessage(...)
    End Try
End Sub
 
Private Sub DataGridLoadNext(Optional ByVal blnSetPoint As Boolean = False)
    Dim intNewAnz As Integer
    Dim intAktAnz As Integer
    Try
        If mblnFirst Then
            mblnFirst = False
            DataGridLoad()
        Else
            If intSatzAnzahl > 0 And intSatzAnzahl < objIBS_Query.lngMaxReadRecord Then
                blnSatzAnzahlEnde = True
            End If
            If blnSatzAnzahlEnde = False Then
                Me.Cursor = Windows.Forms.Cursors.WaitCursor
                intAktAnz = Me.BindingContext(Me.DseDataSetPatient1, "KHSPET0").Count
                intSatzAnzahl = intAktAnz
                objIBS_Query.DataAdapterFillWaiting(objIBS_Query.dadDataAdapterPatient, Me.DseDataSetPatient1, intSatzAnzahl, CInt(objIBS_Query.lngMaxReadRecord), "KHSPET0")
                DataGridFormat()
                If blnSetPoint = True Then
                    If Me.grdDataGrid.RowCount > 0 Then 'hb130103
                        poiPointInCell00 = New Point(Me.grdDataGrid.GetCellBounds(0, 0).X + 4, Me.grdDataGrid.GetCellBounds(0, 0).Y + 4)
                    End If
                End If
                intNewAnz = Me.BindingContext(Me.DseDataSetPatient1, "KHSPET0").Count
                If intAktAnz = intNewAnz Then
                    blnSatzAnzahlEnde = True
                End If
                If intSatzAnzahl > intNewAnz Then
                    blnSatzAnzahlEnde = True
                End If
                intSatzAnzahl = intNewAnz
                Me.Cursor = Windows.Forms.Cursors.Default
                Me.grdDataGrid.Refresh()
            End If
        End If
    Catch ex As Exception
        ErrorMessage(...)
    Finally
    End Try
End Sub

Sometimes this works fine. But sometimes it seems that the scroll event is fired again and again.
Or in some other cases I only get an hourglass and nothing happens.

Any idea what I may have forgotten?