The Ultimate Solution of Excel File Extension is Not Valid Error

Summary: The post highlights a few popular in-built ways to repair a corrupted Excel workbook along with the ultimate solution to resolve the ‘Excel file extension is not valid’ error using a third-party tool which supports both XLS and XLSX versions of the application.

When you open a corrupt Excel workbook, it automatically begins the File Recovery mode. This mode attempts to open and repair the workbook simultaneously. However, at times, the file recovery mode does not open automatically if any issue exists with the workbook. Therefore, it needs to begin in this mode manually to repair the persisting issue. In several cases, if the application is unable to repair the actual concern, some additional solutions can be implemented.

But, before heading towards the resolution methods, let’s understand how to prevent your workbook from getting corrupt. There are some preventive measures that prevent Excel workbooks from becoming corrupt or damaged. Saving the workbook often and creating a backup on a regular basis helps restore data if any damage occurs.

Excel error - File extension is not valid

A common error with workbooks is the ‘Excel file extension is not valid’ error. This error can be repaired in several ways. Let’s look at each:

Manual Repair of Corrupted Workbook

You can repair your Excel workbook manually by performing the following steps:

  1. Click on the File tab and then select Open
  2. Open dialog box will appear; select the corrupt workbook that you wish to access
  3. Click on the arrow button available next to Open and then select Open and Repair
  4. Next, do any of the following options:
    1. Click on Repair if you need to repair the maximum data from the workbook
    2.  Click on Extract Data if you wish to extract values and formulas from the Excel workbook. This is in case the repair workbook does not help

Save Workbook to Last Saved Version

If the Repair method still does not work, you may opt for this method. If you are editing an Excel spreadsheet and your workbook becomes corrupt before it is being saved on your system, you can recover your original worksheet by reverting to the last version. Follow the steps below:

  1. On the File tab, click on Open
  2. Then double-click on the name of the damaged workbook you just opened in Excel
  3. Click Yes to reopen the workbook

Save Workbook in SYLK Format

You may be able to resolve the ‘Excel file format not valid’ error by saving the damaged workbook in SYLK (Symbolic Link) format which helps solve printer corruption. This can be done by performing the steps below:

  1. Go to the File tab and then click on Save As
  2. In Save As, type options. Select SYLK (Symbolic Link) and click on Save
  3. If it indicates that the workbooks containing multiple sheets are not supported by the selected file format, click on OK to save the active worksheet
  4. If a message appears stating that the workbook may contain features that are not supported by the SYLK format, click Yes
  5. On the File tab, click Open
  6. Select .slk file you just saved and click Open
  7. Next, select Save As option from the File tab
  8. In the Save As type dialog box, select Excel Workbook
  9. Next, enter a new name for the workbook to create copy of the file without affecting or modifying the original file and then click on Save


  • When a workbook is saved in SYLK format, only the active sheet is saved
  • To access .slk files, you need to select SYLK Files or All Files in Files of type list
  • All corrupted worksheets need to be saved separately by opening the workbook repeatedly as only active worksheet is saved while saving to SYLK format

If you observed that Excel cannot open the file extension due to file corruption, which has made the workbook data inaccessible, you can then resort to repairing the file using a third-party application.

Stellar Phoenix Excel Repair Tool – An Ultimate XLS / XLSX Recovery Solution

This third-party Excel repair tool is an ultimate solution for ‘Excel file not valid‘ error message. The software repairs almost all types of corruption issues and offers additional benefits while repairing and saving the damaged file. These benefits include:

  • Capable of identifying corruption traces in individual Excel objects
  • Provides option to repair a file or folder
  • Restores recovered Excel file at user defined location on machine
  • Supports both XLS and XLSX file formats effectively
  • Preserves the properties as well as cell formatting while recovery
  • Recovers all Excel contents including table, cell comment, formula, chart sheet, image, filter, sort, etc.
  • Recovered data is stored in a new file, and the original file remains intact
  • Tool is available for both Mac and Windows Excel files

Although the built-in Excel repair procedure offers quite an easy way to deal with corruption, the third-party workbook repair application handles corrupt issues efficiently. The major benefit is that before investing in the full version of the tool, its trial edition can be explored to understand the functionality and check integrity and accuracy parameters. Its trial version allows you to preview the repaired and recoverable data from the corrupted Excel file.

2 thoughts on “The Ultimate Solution of Excel File Extension is Not Valid Error

  1. When AutoComplete runs I want to also automatically copy the contents of the adjacent cell to the right. How do I do this?

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