Problem:






























Solution:

Open Regedit, CTRL+ F... Type in "FileExts" to find this registry location:

"HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts"

Find the file extension you are having problems with. In my example, I used .pl
Expand to view its sub-keys
Delete the sub-key "UserChoice"
Reopen the file... and choose the appropriate program :)