What are you doing to change the background? If you change the background in
the slide master, it will change on all slides. If you check the box for
"Apply to All Slides" it will affect all slides. Also, tell us what version
of PowerPoint you are using.
--David
Are you right clicking to change the background action on the actual slide,
or on the thumbnails on the left? Could all slides be selected somehow when
you click Apply?
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