File association in Windows 10

Windows can only open one program for a particular file type, file extension, automatically. 

So if you like to work with your PNG files in Photoshop Elements, for example, and not Paint, changing the default file association for PNG files is required.

Usually if you double click on a file in the folder and the application will be started if it is not open yet or will be opend by that application.

However, sometimes the double click doesn't work even though the file can be opened by the application itself.

Today while I was checking for a file type belongs to another application in the registry using Regedit.exe, I accidently found the problem why that file type, .prg, cannot be opened by the associated application when double click.

In was a glitch in the registry that the file type 'prg_auto_file' was associated to 3 unreadable registry keys. Remove those 3 unreadable and restart Windows resolve the issue.

16/May/2020 Update

Same thing has happened today again. The prg file associated with Med cannot be opened by double click or drag to Med file area.

Run RegEdit to check .prg_auto_file and those unreadable registry keys are not there. 







Delete these 2 keys in the classes root

1. Computer\HKEY_CLASSES_ROOT\.prg
2. Computer\HKEY_CLASSES_ROOT\.prg_auto_file

Restart the computer. The data value of ProgId in the UserChoice

Computer\HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.prg\UserChoice will change automatically from

'.prg_auto_file' -> 'Applications\\medcx.exe' and this will solve the problem.