If your XLSX file isn’t opening in Excel, you might not have Excel 2007 or a later version, which is needed for XLSX compatibility. Ensure your Microsoft Excel is updated.

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 ...

Key notes A file’s format and extension not matching means the file was saved in a different format than its extension. Problems can occur when trying to open the file if the program doesn’t recognize ...