Excel cannot open the file 'file.xlsx' because the file format

Every now and then, when I try opening an Excel file, I get a message saying that "Excel cannot open the file 'file.xlsx' because the file format or the file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file.

Almir's picture

It also happens due to a bad export or changing file extension

It can happen also due to inappropriate export. Maybe the file was exported to Excel in inappropriate manner. Anther reason could be manual changing of extension.

I see this most often when a file has been transferred around a

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?

Reinstall Office? Try XLSX Open File Tool for recovery your documents (http://www.xlsx.openfiletool.com/)
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