Excel VBA Run-time error 2147188160 (80048240) Automation Error

Question

This is more a set of comments than an answer, but the comment fields don't allow for any reasonable formatting. See comments in-line:

   Sub CreateSlides()
    Dim aData As String
    Dim newPPT As PowerPoint.Application
    Dim Actslide As PowerPoint.Slide
    Dim Actshape As PowerPoint.Shape

' SlideHeight and Width are Singles, not Longs
    Dim lngSlideHeight      As Long
    Dim lngSlideWidth       As Long

' Here, you've DIMmed all of the variables as variants, not integers:
    Dim i, x, rowcount, slinum, slicount As Integer
' You really want:
'   Dim i as Long, x as Long ....etc.
'   Note that most if not all of these should be longs, not integers
'   Generally, VBA will convert for you as needed, but once in a while it'll
'   turn round and bite you.  Better to use the correct data types in the first place.

    Dim Size As Integer

Set newPPT = New PowerPoint.Application
' I'd move this here rather than below:
newPPT.Visible = msoTrue

newPPT.Presentations.Add
newPPT.ActivePresentation.Slides.Add newPPT.ActivePresentation.Slides.Count + 1, ppLayoutBlank
' newPPT.Visible = msoTrue

lngSlideHeight = newPPT.ActivePresentation.PageSetup.SlideHeight
lngSlideWidth = newPPT.ActivePresentation.PageSetup.SlideWidth

ActiveSheet.Cells(1, 1).Select

' Check what UsedRange returns against what you THINK it's supposed to return.
' Sometimes it's not quite what you expect:
rowcount = ActiveSheet.UsedRange.Rows.Count

' No need for either of these; the For/Next syntax takes care of that
'slinum = 1
'x = 1

'create slides
For slinum = 1 To 2 * rowcount + 10
    Set Actslide = newPPT.ActivePresentation.Slides(slinum)
    newPPT.ActivePresentation.Slides.Add newPPT.ActivePresentation.Slides.Count + 1, ppLayoutBlank
Next slinum

'copy words
slinum = 1
x = 1
For x = 1 To rowcount

    ActiveSheet.Cells(x, 1).Select
    Selection.Copy
    newPPT.Visible = True

    newPPT.ActiveWindow.View.GotoSlide (slinum)
    newPPT.ActiveWindow.Panes(2).Activate
    Set Actslide = newPPT.ActivePresentation.Slides(slinum)
     newPPT.ActiveWindow.View.PasteSpecial DataType:=ppPasteDefault

    newPPT.ActiveWindow.Selection.ShapeRange.Top = (lngSlideHeight - newPPT.ActiveWindow.Selection.ShapeRange.Height) / 2
    newPPT.ActiveWindow.Selection.ShapeRange.Height = 400
    newPPT.ActiveWindow.Selection.ShapeRange.Left = 1
    newPPT.ActiveWindow.Selection.ShapeRange.Width = lngSlideWidth - 1
    newPPT.ActiveWindow.Selection.ShapeRange.TextFrame.TextRange.ParagraphFormat.Alignment = ppAlignCenter
    newPPT.ActiveWindow.Selection.ShapeRange.TextFrame.TextRange.Font.Size = 48

        If slinum Mod 9 = 0 Then
            slinum = slinum + 9
        End If

    slinum = slinum + 1
Next x

slicount = 2 * rowcount + 10
slinum = 10
x = 1
i = 1
For x = 1 To rowcount

    ActiveSheet.Cells(x, 2).Select
    Selection.Copy
    If i = 1 Then
        newPPT.Visible = True
        newPPT.ActiveWindow.Panes(2).Activate
        newPPT.ActiveWindow.View.GotoSlide (slinum + 2)
        Else
            If i = 2 Then
            newPPT.Visible = True
            newPPT.ActiveWindow.Panes(2).Activate
            newPPT.ActiveWindow.View.GotoSlide (slinum)
            Else
                If i = 3 Then
                newPPT.Visible = True
                newPPT.ActiveWindow.Panes(2).Activate
                newPPT.ActiveWindow.View.GotoSlide (slinum - 2)
                End If
            End If
    End If
    i = i + 1

    If i = 4 Then
        i = 1
    End If

    newPPT.ActiveWindow.View.PasteSpecial DataType:=ppPasteDefault
    newPPT.ActiveWindow.Selection.ShapeRange.Top = (lngSlideHeight - newPPT.ActiveWindow.Selection.ShapeRange.Height) / 2
    newPPT.ActiveWindow.Selection.ShapeRange.Height = 400
    newPPT.ActiveWindow.Selection.ShapeRange.Left = 1
    newPPT.ActiveWindow.Selection.ShapeRange.Width = lngSlideWidth - 1
    newPPT.ActiveWindow.Selection.ShapeRange.TextFrame.TextRange.ParagraphFormat.Alignment = ppAlignCenter
    newPPT.ActiveWindow.Selection.ShapeRange.TextFrame.TextRange.Font.Size = 28

        If slinum Mod 9 = 0 Then
            slinum = slinum + 9
        End If

        If slinum > slicount Then
            Exit For
        End If

    slinum = slinum + 1
Next x


End Sub