A girlfriend has a problem with ACDSee (for Pentax). For some reason it has been set as the default application for opening folders, so everytime a folder is clicked, ACDSee opens. If already tried to fix the file association (changing the default action, adding a new action that opens explorer, but it won't work ).
I've also tried to untick the "browse with acdsee" option in ACDSee, but it doesn't remember this option.

How can I fix this ?

Can you explain just a tad more? Does this happen when you open My Computer > C: > Some Folder? Or does it happen when AutoRun is detected by a CD, DVD, or removable media? If it is the first then I have no idea, I have never heard of such a thing happening and I don’t know if it is even possible (it is if this is the case but I digress).

The second problem can be fixed by configuring AutoRun. Windows XP and Vista (I can’t remember if 2000 also) use a formula to tell how to open an AutoRun item. Vista is slightly different than XP but they are basically the same. If the documents are mostly pictures then a picture viewer is used, for music the music formatting is used. One of the first things I do to a new computer is turn off all AutoRun options for all drives. I consider it a security issue and I don’t like the idea of a random CD executing code on my machine without permission. The tool that I use is TweakUI (http://www.microsoft.com/windowsxp/downloads/powertoys/xppowertoys.mspx) from Microsoft. While looking over my copy of TweakUI, I noticed the following tip

“To Customize AutoPlay settings, open My Computer, right-click the drive you want to customize, select Properties, then AutoPlay”

Those instructions may be exactly what you are looking for but I would suggest you also take a look at TweakUI and see if there is anything useful to you in there (like disabling AutoRun all together).

The problem is that ACDSee opens everytime a drive or folder is double-clicked.
I've already managed to fix the problem for drives (by changing the default action), but it doesn't want to work for folders . Maybe it has something to do with the fact that 3 users were loged on to the computer, but I doubt that'll be the problem.

I don't know when I have the chance to try fixing it, but I think I'm going to uninstall and reinstall the application first before trying again. If I find a solution, I'll post it here .

Once you get it fixed for one folder you can always apply the changes to all folders. Lets say you have it fixed for the C: drive, go to Tools > Folder Options… > View > Click Apply to All Folders. This still has to be the strangest things I have heard and I would love to know how you fix it. Better yet I would love to know how it happened in the first place.

I fixed this problem by changing the setting of ACDSee
Problem With Acdsee

AcdSee > Tools > Film Associations > Shortcut Menu > Folder > Uncheck "Brose with AcdSee"

-reply by Kingbird