Unable to change Default Program Extension on Windows 10/8/7

Today, I’m going to show you a way out, if you ever face a situation, where you cannot or are unable to change the default program extension in Windows 10/8/7. I was helping out a client of mine. His operating system had somehow changed the default program extension to a different program; i.e. the file was supposed to open with Outlook – but instead it change into Notepad.

Unable to change Default Program Extension

When I tried to change it back to Outlook under Properties of that file the change option was grayed out


So I tried to right-click on the file and clicked on “Open With” dialog box, because there you have a change box “Always use the selected program to open this kind of file”.

But strangely that check box was grayed out, as well. When I select Outlook, it opens fine. But I was just unable to set it as the default option.

So I went to Control Panel\All Control Panel Items\Default Programs\Set Associations and tried to change it there; but sadly I was again unable to. I was totally stumped because the UAC was turned off, the user is a Windows administrator – so there was no reason for the option to be disabled.

That’s when I remembered that there is an option in Windows registry, where you can change it. So I opened the registry and navigated to the following key:


Here you have to find your extension under a key called “UserChoice”.

What this registry key does, is if you change the Default file extension, Windows creates this key and adds the value there.

On the Right hand side you’ll seestring value “Progid” under that value you’ll see the current program that is associated with it. So I tried to change that value but it gave me an error: Cannot edit Progid.


Now I realized what was wrong! For some reason, that specific registry key doesn’t have permission to change the file extension, and that was the reason why those options were grayed out for me. So I took ownership for the parent key  and inherited the permission.


Now I could delete the “UserChoice” key. Once I deleted it and I rebooted the system. And voilà – now I got this window!


Once I selected the correct program I made it as default and it stayed.

Hope this becomes helpful for someone who runs into a similar problem.

These links may also interest you:

  1. File Association Fixer for Windows 7
  2. Default Programs Editor for Windows 7
  3. Remove unwanted programs from Recommended Programs List in the Open With box
  4. How to dissociate File Types in Windows.
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Shyam aka “Captain Jack” is a Microsoft MVP alumnus and a Windows Enthusiast with an interest in Advanced Windows troubleshooting. Suggestions made and opinions expressed by him here are his personal one's and not of his current employers. He blogs at captaindbg.com.