Excel cannot be open the file 'filename.xlsx' because the file format or file extension is not valid

Here are suggestions from MS Copilot:

This error usually occurs when Excel cannot recognize the file format or extension. Here are a few steps you can take to troubleshoot and resolve this issue:

1. Check the File Extension:
   • Ensure that the file has the correct .xlsx extension. Sometimes, renaming the file with the correct extension can resolve the issue.
2. Verify the File Format:
   • Make sure the file is indeed an Excel file. If the file was saved with a different format but has an .xlsx extension, Excel might not be able to open it.
3. Open with a Different Program:
   • Try opening the file with a different program, such as Google Sheets to see if the file is recognized and can be opened. If it opens, you can save it again as an Excel file.
4. Repair the File:
   • Open Excel, go to File > Open, and select the file. Instead of clicking Open, click the arrow next to it and select Open and Repair. This can sometimes fix issues with the file.
5. Check for Corruption:
   • The file might be corrupted. If you have a backup, try opening the backup file. If not, you might need to use a file recovery tool to attempt to repair the corrupted file.
6. Update Excel:
   • Ensure that you are using the latest version of Excel. Sometimes, updates can resolve compatibility issues with certain file formats.
7. Check File Size:
   • If the file size is unusually small (e.g., 0 KB), it might indicate that the file is empty or corrupted.
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