Older versions of PowerPoint (2000 and earlier) do not support multiple masters. If you will be working on a presentation in older versions, you should disable multiple masters.
- Choose Tools → Options and click the Edit tab.
- In the Disable new features section, clear the Multiple masters check box to enable multiple masters, or check the option to restrict design templates to one per presentation.
If your presentation already has multiple masters and you want to work with the presentation in an older version of PowerPoint, you should disable multiple masters (as described above), then select one of your presentation's design templates and choose Apply to All Slides. This will replace the multiple masters in your presentation with the single, selected design template.