LaTeX.org

Thanks for your reply but I'm on a Mac with MacTex... Do you have any idea how to restore the setting there, too?

I have a similar problem. I wanted to install an additional class (Mac, MacTex), and put it in the user folder (~/texmf/ ...). Afterwards LyX couldn't find any classes any more. Even after completely deleting the user texmf folder and performing a texhash or reinstalling LyX, none of the classes ...