built in games lost executable association

Hi, When I now try to start a game from the game folder, a messagebox appears, saying: This file does not have a program associated with it for performing this action. Create an association in the Folder Options control panel.
The title of the message is absolute path to the .lnk file of the game.
Any other links - from the start menu, desktop links and so on, work as usual. If I start the shortcut whose path is in the message box title, it gets executed.
Change what I've done is removed the IsShortcut from the lnkfile class in the registry in order to hide the shortcut arrows. If this is the issue, why clicking on the .lnk files works?
Any idea what's happening here and how to repair it? Jan