One common challenge that users face is encountering the error message Excel cannot open the file because the file format or file extension is not valid .

With the Excel extension is not valid error, try starting the app in Safe Mode, repair the workbook or open the file in another program.

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.

The file format or file extension is invalid. Verify that the file has not been corrupted and that the file extension matches the format of the file." Using Excel for Mac 2011, Version 14.3.9 and t ...

In the Files Of Type list, click the file type you’re trying to open, in this case Excel (*.xl*), highlight the file by clicking it, and then click Open. If the Excel spreadsheet you’re trying to view ...