Each presentation is generated from a single excel template file we deploy. What happens if you double click on it in File Explorer?  If you don't have it, but do have th ExcelPresentation.xls.bak.. open Excel, and then Open that one.

I have seen cases where Microsoft decides to "protect" the excel file - it'll have a big red "Protected View" across the bar.  If that's happening we'll need to figure out how to remove that. I can look into it if you confirm.