Convert the .xls workbook to .xlsx and upload the converted copy to OneDrive; Excel for the web can view .xls files but converts them to .xlsx for editing.^1^
Convert the file
- In OneDrive on the web, select the file, then choose Download.
- Keep the original
.xls file as a backup.
- Open the downloaded file in the Excel desktop application.
- Select File → Save As.
- For Save as type, select Excel Workbook (
.xlsx) and use a new filename.
- Upload the new
.xlsx file to OneDrive and open it in the browser.
Important: If the workbook contains macros, saving it as .xlsx removes them. Preserve the original and use a macro-enabled format if the macros are required.
If the downloaded file will not open
That points to a problem with this workbook rather than the OneDrive webpage. In desktop Excel:
- Select File → Open → Browse.
- Select the downloaded
.xls file.
- Select the arrow beside Open, then choose Open and Repair.
- Choose Repair first.
- If repair fails, repeat the process and choose Extract Data to recover available values and formulas.^2^
- Save the recovered workbook under a new
.xlsx filename and upload it to OneDrive.
Do not simply rename .xls to .xlsx; changing the filename extension does not convert the underlying workbook format and can produce a format-mismatch error.^3^
If only the browser fails
Test another known-good Excel file in the same OneDrive account:
- Other files open: the affected
.xls file likely needs conversion or repair.
- No Excel files open: try an InPrivate/Incognito window or another current browser. If that works, disable browser extensions for OneDrive or clear the browser’s cached data and cookies; browser cache and extensions can interfere with Excel for the web loading.^4^
- The converted
.xlsx still fails in multiple browsers: use OneDrive’s support option and provide the filename, approximate file size, browser name, and the exact “Sorry, an error has occurred” message.
References
- Office for the web service description
- Repairing a corrupted workbook
- A file is in a different format than its extension indicates in Excel
- Failed to open a file on web Excel which has no previous version. - Microsoft Q&A