How do you produce (or try to produce) LaTeX/pdf?The Unknown LaTeX class message is something emacs throws when using export to latex (C-c C-e l l). This has nothing to do with your LaTeX installation; it does not reach the point of invoking LaTeX. It tells you there's no setup for scrlttr2 class in org-latex-classes. There is no setup for default-koma-letter either in my version of org-latex-classes. Perhaps you need to load ox-koma-letter in org first?
HTH, Julius
