Need expert help with file association changes via registry


Senior Member
For some unknown reason, my image file associations in Windows Explorer keep getting undone, such that they show up in Explorer without an associated application (or occasionally with a wrong association).

For example, when I examine the properties of any .jpg file, the "Open With:" property says "Unknown application".

My default image file viewer application is ACDSee Ultimate 8, and the registry key for .jpg files looks like this:


"ACDSee Ultimate 8.jpg"=hex(0):

"Progid"="ACDSee Ultimate 8.jpg"
However, as I say, that never seems to get propagated from the registry such that Explorer will correctly open ACDSee when I double-click an image file (ALL image files are the same, not just .jpg). The question is: WHY?

I've tried creating a .REG file that contains all the correct registry settings, but when I merge it, nothing actually changes!

And naturally I've tried running the following command to force the registry to be freshly loaded:

C:\Windows\System32\rundll32.exe USER32.DLL,UpdatePerUserSystemParameters ,1 ,True

But nothing seems to work!

I trust you've seen that I'm a very knowledgeable user who is not struggling with primitive questions, but I'm at a loss. What, exactly, am I doing wrong? What do I have to do to FORCE a change to all the file associations such that they'll open in ACDSee when I double-click them?


Honorable Member
I navigated to the registry address on my computer ...\FileExts\.jpg as in the first line in your above list, the MRUlist has many entries with one being DLLhost.exe for some reason? Maybe it's something to do with ACDsee? Also above it says: "a"="ACDSeeUltimate8.exe" then: "ACDSee Ultimate 8.jpg" note the gaps, couldn't be that perhaps?

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