Application-defined or object-defined error

[dverga]

I'm very new to VBA.
I'm trying to copy some charts into a pptx template, using this basic code:

Option Explicit
Sub CreatePowerPointTemplateM4()
Dim PowerPointApp As PowerPoint.Application
Dim PowerPointPrsn As PowerPoint.Presentation
Dim Chrt As ChartObject
Dim strpath As String

strpath = ThisWorkbook.Path & "\My_Template.pptx"

Set PowerPointApp = New PowerPoint.Application
Set PowerPointPrsn = PowerPointApp.Presentations.Open(strpath)

' get chart #5 and copy it into slide #7
Set Chrt = Worksheets("Graphs").ChartObjects(5)
Chrt.Copy
DoEvents
PowerPointPrsn.Slides(7).Shapes.PasteSpecial DataType:=ppPasteMetafilePicture
End Sub

This code has worked on my laptop for a few days. Now I get Run-time error '1004': Application-defined or object-defined error.
How is it possible??
The Chrt variable is defined as Chart.Object and it does contain the Copy method.

Many thanks to whom can solve this!