When attempting to open or edit an Excel file in MS Office 2003/2007/2010/2013/2016/2019, several users have reported about receiving ‘Excel cannot open the file because the file format or file extension is not valid’ error message.

The complete error message reads as follows:

"Excel cannot open the file 'filename.xlsx' because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file."

Excel file extension error

                                    Figure 1 - Excel File Extension not Valid Error Message

In this post, we will outline common reasons behind the error and discuss some effective solutions to resolve the .xlsx error. We will also explain how you can get your MS Excel data back. 

What Causes ‘Excel File Extension not Valid’ Error?

The error may occur due to any of these reasons:

  • The file is not compatible with the MS Excel version
  • The Excel file is corrupt or damaged

How to Fix ‘Excel File Extension not Valid’ Error?

Note: Before using the methods discussed below, try opening your Excel in safe mode. If the file opens in safe mode, chances are that add-ins issues might be preventing the file from opening. So, try disabling the add-ins one-by-one to see if the error is resolved. 

Try the below-mentioned methods to resolve the ‘Excel cannot open the file because the extension is not valid’ error, and regain access to the Excel worksheet:

Method 1 – Change the Default File Format to Save Excel Workbooks

MS Excel saves workbooks as XLSX or XLS file format by default. In Excel 2003 and earlier versions, files are saved as XLS. On the other hand, the files get saved in XLSX file format in Excel 2007, 2010, 2013, 2016, and 2019 versions. You may encounter the error ‘Excel file extension not valid’ due to an incompatible Excel file extension.

To resolve the issue, try changing the respective Excel version's default file format to any other file format that MS Excel supports. To do so, execute the following steps:

  • In Excel 2007, click the ‘Microsoft Office’ button and then ‘Excel Options’. In Excel 2010 and higher versions, click File > Options.
  • Select Export option.

Export File

                                                                Figure 2 - Select Export Option in Excel

  • Select Change File Type option.

Change File Type

                                                                                     Figure 3 - Change the Excel File Type

  • Change the file extension, and then click Save As.

Now check if Excel can open the file.

Method 2 – Recover Unsaved Workbook

If you encounter the ‘Excel file extension not valid error’ when trying to open an unsaved workbook, try these steps to recover the unsaved workbook:

  • Go to File and select Info option.
  • Under Manage Versions, select ‘Recover Unsaved Workbooks’ op

recover unsaved workbook

                                                              Figure 4 - Recover Unsaved Workbooks Option in Excel

  • If MS Excel has unsaved files then, it will list them. You can open and save it.
Note: The unsaved files default location is:
C:\Users\dazy.parker\AppData\Local\Microsoft\Office\UnsavedFiles


Method 3 – Use 'Open and Repair' Feature of MS Excel

 The ‘Open and Repair’ is a built-in Excel utility, designed to repair damaged Excel files. To use it, perform the following steps:

  • Open MS Excel application.
  • Go to File and Select Open option.
  • Select the corrupt file and choose Open and Repair option.

Open and Repair Option

                                                                          Figure 5 - Excel Open and Repair Feature

  • Click Repair to start repairing the file.

Repair Excel file

                                                                            Figure 6 - Repair the Microsoft Excel File

Note: If the Excel repair process was not successful the last time you used the ‘Open and Repair’ feature, repeat the Steps (1) to (4). Next, click the ‘Extract Data’ button to extract the Excel file's values and formulas.


Method 4 – Use an Excel Repair Software

If the above manual methods fail to fix the “Excel cannot open the file '(filename)'.xlsx…” error, repairing the file using a specialized Excel repair software may help.

Stellar Repair for Excel software is purpose-built to repair corrupt XLS and XLSX files. The software also helps restore entire file items such as table, chart, chart sheet, image, cell comment, formula, sort, filter, etc., maintaining the original format of the MS Excel files. 

free download

Check out the video to know how to repair corrupt Excel file by using Stellar Repair for Excel: 

End Note

Several manual methods, such as the ones discussed in this post, can help fix the ‘Excel cannot open the file ‘(filename)’.xlsx’ error. We recommend using the Stellar Repair for Excel software discussed above to resolve the error when other methods fail. Use the demo version of the software to ascertain its functionality by previewing the recoverable Excel data.