Why can't change the default program to open an extension in Windows 7?

"Windows Vista and Windows 7's file type management facilities are half-baked at best. I never understood why Microsoft crippled that part of the OS when they released Vista. They added limitations that make absolutely no sense.

You might want to try to use alternatives listed in my previous question on the matter:

What program do you use to edit file associations in Vista and Windows 7?

The program that stood out was Default Programs Editor which is free and will allow you do pretty much whatever you wish to do."

"To change an extension to not be opened by any program:

Create a text file with a line of gibberish in it.
Save to your desktop with the .txt extension.
In Control Panel, go to the extension for which you want to remove the default association.
Assign the above text file to be the default program for that extension.
Close Control Panel.
Go back to the text file and delete it.

The extension that was associated with this text file in step 4 will now show it is associated with an ""unknown"" program."

Since the registry entry may be botched, another way to fix this might be to run a registry cleaner (I used Eusing Free Registry Cleaner) that will detect an invalid entry and delete it. Afterwards, you can try again to associate the extension the normal way. This worked for me, after I had switched from a portable to a system installation, and the registry still pointed to the portable installation.

"Is ""NoFileAssociate"" set to 0?

From KB555076:

Go to ""Start"" -> ""Run"".
Write ""Regedit"" and press on ""Enter"" button.
Navigate to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\Explorer
In the right side of the screen double click on ""NoFileAssociate"".
Change the value of ""NoFileAssociate"" from 1 to 0.
Close ""Regedit"".
Reboot the server."

"Let me share a related experience with my Win7 PC. My PC had two email clients installed Lotus notes and Outlook 2013. Had set outlook as the default to open all email related extensions such as .eml, .msg, .vcf, .vcs etc. However .eml files were not opening when i double clicked on a file with .eml extension. Had to use the ""open with"" option to open such files in outlook.
Hence i went to control panel - ""Set default programs"" - ""Outlook""- ""choose defaults for this program""- and checked the .eml option. However on going back the check box for .eml files had cleared itself.

Solution: Found the below reg key
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts.eml]
Deleted the .eml key. Double clicked the .eml file and it opened in outlook , also the .eml option got checked in ""Set default programs"" for outlook in control panel."