Different background transparency when presentation opened then Run from when Viewed

[JMB]

I made up a very simple Powerpoint 2007 presentation displaying some forthcoming events. I added a background image on a few slides and adjusted the transparency so the image was quite feint and the text easily readable.

This worked fine when I opened the file from within Powerpoint then the Slide Show run.

Later I just double-clicked the file name to view the slide show and found that the background images were not at all transparent so the text was hardly readable.

Is there a way around this problem

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