Stephan, maybe you are right. When I click on the plug in icon in applications i get a note "Could not complete your request because photoshop doesn't recognize this type of file". What do yo make of this message? It sure is fun talking to you guys. What a miracle the internet is!
I would ask you to confirm the following two points:
1) Please state for the record your Mac hardware (PPC or Intel), operating system version and Photoshop version or Photoshop Elements version.
2) Select the plug-in file in the Finder, CMD I or "File/Get Info" on the plug-in...does it look like the screen capture below? Even better, do a screen capture and attach it to your reply!