Presenter was unable to open project file

I worked all day today adding audio to a presentation.  I had published it and viewed it several times today.  Tonight when I closed out of PowerPoint and then went back in, I went to open the file from my most recent list, and it comes up, but if I choose to preview a slide, I get the error:

Presenter was unable to open project file

I am new to this product, but I have successfully created many presentations and never have I experienced this.  HELP!

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