What’s causing the ‘File Format and Extension of Don’t Match’ error?
Method 1: Changing the extension manually
In most cases, the error message is pointing to the right cause. If you see the ‘File Format and Extension of Don’t Match’ error, the Excel file you are trying unsuccessfully to open is likely in fact of a different extension that the one that is currently hardwired. Several affected users that were also encountering this issue have reported that they managed to fix the problem by manually changing the extension (via renaming) to various popular Excel formats until they found the correct one. Here’s a quick guide on how to do this:
Method 2: Unblocking the file (if applicable)
As it turns out, the ‘File Format and Extension of Don’t Match’ error can also occur because it’s being blocked at a Properties level. This is a typical occurrence with files downloaded over the internet or received via email attachments as a security option. If this scenario is applicable, you can resolve the issue very easily by accessing the Properties screen of the file that is triggering the error message and unblocking it via the Security tab. Here’s a quick guide on unblocking excel files that are triggering ‘File Format and Extension of Don’t Match’ errors at launch: If the same ‘File Format and Extension of Don’t Match’ error is still appearing, move down to the next potential fix below.
Method 3: Opening the file with a 3rd party equivalent
Several affected users that were also encountering this issue have confirmed that they were finally able to open the Excel file and edit without encountering the ‘File Format and Extension of Don’t Match’ error by installing a free Excel equivalent and using that to open the problematic file. As it turns out, this operation might end up avoiding corrupted instances that ultimately make the file unopenable. And if you decide on using OpenOffice, it’s notoriously known for being way better at eliminating corrupted attachments from Excel files when migrating them to the .ODS format. Here’s what you need to do to open the file with a 3rd party equivalent: If the ‘File Format and Extension of Don’t Match’ error is still appearing or you’re looking for a different fix that doesn’t require the installation of other 3rd party components, move down to the next method below.
Method 4: Disabling Protected View
As it turns out, the ‘File Format and Extension of Don’t Match’ error will often occur because a fairly new security option (Protected View) is preventing the Excel application from opening up certain files that were obtained through email attachments. If this scenario is applicable, you can bypass this security option by accessing your Excel settings menu and disabling the Protected View feature altogether. Several affected users that were also affected by this issue have confirmed that the issue was completely resolved. Here’s a quick guide on how to disable Protected View from your Excel settings: Note: The steps below should work for every recent Excel version (2010 and above). If the same File Format and Extension of Don’t Match error is still occurring, move down to the next method below.
Method 5: Suppressing the warning message
If none of the methods above have allowed you to fix the File Format and Extension of Don’t Match error message, and you don’t want to update your Office installation to a newer version where the issue is resolved, you also have the option to create a registry key that is capable of suppressing the warning error message altogether. But before you do this, keep in mind that going this route might leave your system vulnerable to exploits in the future. But in case the affected computer is part of an organization network, it should not affect you in any way. Here’s a quick guide on suppressing the File Format and Extension of Don’t Match error message by using Registry Editor:
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