Hi Felix & NightCabbage - hmm I'm not sure how you would fix that.

File associations are actually stored in the registry though, do you possibly have some kind of strict permissions set on your registry or something like that?

On Windows 7 you might try turning off UAC temporarily and then see if you can set the file assocation ok or not.

Otherwise you might try setting it directly in the registry, looks like there are some notes on that here: http://answers.microsoft.com/en-us/windows/forum/windows_7-files/problems-with-file-association-in-windows-7-64-bit/8a84fcec-22df-4942-8e35-d98dbe96e327

- Michael