Excel: “We found a problem with some content”

Excel says “We found a problem with some content in … Do you want us to try to recover as much as we can?”, or “Excel cannot open the file because the file format or file extension is not valid.” The numbers you need are often still in there.

What's inside an .xlsx

An .xlsx file is a zip folder holding one file per sheet, plus a shared list of all the text in your cells, the formatting, and a table of contents. Text cells don't hold their text directly: they point at an entry in the shared list. If that list is cut short, or a sheet's file is damaged, Excel can refuse the whole workbook.

Common causes

The file was saved while the computer crashed or a USB drive was removed.
A download, email attachment or OneDrive/Dropbox sync stopped part-way.
A program that exports to Excel (accounting or reporting software) wrote something Excel doesn't accept.

Free things to try first

Click Yes when Excel offers to recover what it can, then check what it removed.
File → Open → Browse, select the file, click the arrow next to Open, and choose Open and Repair. If repair fails, run it again and pick Extract Data.
Look for an earlier version in Properties → Previous Versions or in OneDrive version history.
Try opening it in LibreOffice Calc or Google Sheets.

When Excel's repair fails

Office File Repair takes the workbook apart and keeps every sheet it can read. It rebuilds the table of contents, cuts damaged sheets back to the last complete row, and leaves cells empty only where their text was truly lost. You get a fresh .xlsx that opens normally.

The preview shows the recovered rows before you pay, and nothing is uploaded: it runs in your browser.

Check your spreadsheet: the preview is free