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I have an issue with a custom file extension that I've added in the registry, I've followed all steps, reviewed the .ico file path, deleted the associated registry entries and tried again, rebooting Windows and nothing.

Due I have low reputation points I can't add an image, but the file with the custom extension has an icon with the white sheet and the application icon in the center of it.

The extension is .mqs and it's in the registry as .mqs with MQSFile value in HKEY_CLASSES_ROOT, and the second key named MQSFile in HKEY_CLASSES_ROOT default value is "Encrypted MQS script" and DefaultIcon value has the icon path "C:\Program Files\MQS\resources\folder_icon.ico"

So what's wrong, the registry keys? Or the icon cache?

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You make it in the DefaultIcon default value.

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\MQSFile\DefaultIcon]
@=PATH TO ICON IN HEX or BINARY

Example, regedit icon for .reg files.

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\regfile\DefaultIcon]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
  00,5c,00,72,00,65,00,67,00,65,00,64,00,69,00,74,00,2e,00,65,00,78,00,65,00,\
  2c,00,31,00,00,00

Value decoded

%SystemRoot%\regedit.exe,1

The comma, one is the icon position in-case of multiple icons.

  • so if you are confident this is correct in your app, we should flush the icon cache, what OS are you on XP, W7, W8 ??? – Knuckle-Dragger Dec 18 '13 at 18:19
  • C:\Users\KNUCKLE-DRAGGER\AppData\Local\IconCache.db on my W7, probably safer to delete while logged as a different user. – Knuckle-Dragger Dec 18 '13 at 18:22
  • Thanks, in your answer just noted that DefaultIcon must be a subkey and not the value in MQSFile! I have Windows 7, sorry for not adding that info! And to update icon cache just used ie4uinit.exe -ClearIconCache – FukYouAll Dec 18 '13 at 18:42

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