While programming PowerPoint 2007 in .Net, when you try setting Footer text for slides, you may encounter the following error message,
HeaderFooter (unknown member) : Invalid request.
This is a known issue and has been reported to the product group
To workaround this issue, first, we need to set the “Visible” property of the footer object to true and then we need to set the footer text.
PPTApplication.ActivePresentation.Slides.HeadersFooters.Footer.Visible = Microsoft.Office.Core.MsoTriState.msoTrue; //Here PPTApplication is object of PowerPoint.ApplicationPPTApplication.ActivePresentation.Slides.HeadersFooters.Footer.Text = "My Text";