Today I was working with someone and thought we had a permissions problem opening a .DLL file in a particular directory. I had them open the file with notepad.exe to check to see if they had rights. Before I could warn them about the checkbox to always open .DLLs with notepad they had clicked on the OK button.

I wanted to clean up the association so they wouldn’t accidentally open and save a .DLL causing some kind of hard to track down corruption. I did some searching and found a lot of people talking about how to associate files with a particular program by either right clicking on the file and going through the open process to get to the point where they could choose a program (like we did) or through Control Panel –> Default Programs –> Associate a file type or protocol with a program but very few explaining how to remove the file associations.

I found this process and it worked for me. Of course all of the standard disclaimers about changing the registry also apply here.

If you open regedit and navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.dll you will see that there are three keys.

I deleted the OpenWithList and UserChoice keys.

Under the OpenWithProgids key I didn’t need to make any changes. The key had a default value and a REG_NONE value named dllfile.

This fixed the association for me and I haven’t seen any issues with the changes.