Common Issues and Workarounds with Excel File Formats
This page contains information on common issues with Excel file formats, as well as workarounds to help address them.
Excel Extension Mismatch Warning
A warning of an extension mismatch may appear when exporting a file to Excel, as displayed in the figure below:
Possible “File Format and Extension don’t Match” error causes
Incorrect extension – in most cases, this issue occurs because the Excel file is of a different format than its extension shows. This may happen automatically after the file is converted, or manually, after a user intervention. In such a case, the issue can be fixed by changing the extension manually to a correct one.
Excel file is blocked – if the Excel file was obtained from an e-mail attachment, it may be set to Blocked in the file’s properties. Many e-mail providers block such files automatically for security purposes. In such a case, unblock the file in its properties.
The file is incompatible with Excel – This issue may occur due to its incompatibility with Excel. To resolve this issue, try to open the file with other spreadsheet software, such as OpenOffice Calc.
Protected Views is enabled – A security option may prevent Excel from opening certain files, such as those that are received as email attachments. To resolve this issue, open Excel settings and disable Protected Views from the Trust Center menu.
The message is not disabled – To avoid updating your Office to the latest version in which this issue is resolved, it is possible to circumvent the error by disabling the warning message. In such a case, use the Registry Editor to create an ExtensionHardening value.
Method 1: Changing the extension manually
Open File Explorer and select the View tab. On the ribbon, ensure that File Name Extensions is enabled