I’ve successfully followed these steps:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts[fileextension]\OpenWithList. and deleted the unwanted file.

Then I checked the Recommended Program List for .Dll file. But the unwanted program was still there in list. So I thought changes might be reflected after reboot. But even after reboot it was showing the program in list.

I’ve again confirmed that key is deleted. So what’s wrong?