Solution 7: Open MS Excel in Safe Mode Solving the “ Excel cannot open because the file format is not valid ” problem can sometimes be as simple as booting your computer into Safe Mode . This is ...

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.

To fix the Excel file format does not match extension error, trying opening the spreadsheet with the Open and Repair option or changing its file extension.

[Bug]: Excel cannot be open the file because the file format or file extension is not valid #3987 Closed ruuddeenen opened on Aug 31, 2023 ...