Windows

I see this most often when a file has been transferred around a lot and gets corrupted due to bad sectors on hard drives,
bad thumb drives, etc...
Occasionally, I find a repair utility that will....kind of....fix it. You tend to lose all formatting and usually the user

would have to spend more time doing than life than simply starting from scratch. If on a file server, shadow copies

(previous versions) are a god send.
If it happens completely randomly, does it happen more often to the same group of people? Perhaps an update malfunctioned?

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There could be so many reasons this could happen, but all the above is where I'd start.
Also read this https://groups.google.com/forum/#!topic/xlsx-viewer-download/Yf8eudHMWv8

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