>>> "Josiah" == Josiah Schwab <jschwab@gmail.com> writes:

   > Hi Uwe,
   >> Now I took the example
   >> https://orgmode.org/manual/A-Beamer-example.html#A-Beamer-example
   >> 
   >> And wanted to export it to beamer but obtained the message 
   >> user-error: Unknown LaTeX class ‘beamer’

   > This sounds to me like you are using the latex exporter, rather than the
   > beamer one.

   > After

   >   (require 'ox-beamer)

My problem can be caused that I have used custom to add the exam class.
So my relevant custom entries looks like

 '(org-latex-classes
   '(("article" "\\documentclass[12pt]{article}"
      ("\\section{%s}" . "\\section*{%s}")
      ("\\subsection{%s}" . "\\subsection*{%s}")
      ("\\subsubsection{%s}" . "\\subsubsection*{%s}")
      ("\\paragraph{%s}" . "\\paragraph*{%s}")
      ("\\subparagraph{%s}" . "\\subparagraph*{%s}"))
     ("report" "\\documentclass[12pt]{report}"
      ("\\part{%s}" . "\\part*{%s}")
      ("\\chapter{%s}" . "\\chapter*{%s}")
      ("\\section{%s}" . "\\section*{%s}")
      ("\\subsection{%s}" . "\\subsection*{%s}")
      ("\\subsubsection{%s}" . "\\subsubsection*{%s}"))
     ("book" "\\documentclass[12pt]{book}"
      ("\\part{%s}" . "\\part*{%s}")
      ("\\chapter{%s}" . "\\chapter*{%s}")
      ("\\section{%s}" . "\\section*{%s}")
      ("\\subsection{%s}" . "\\subsection*{%s}")
      ("\\subsubsection{%s}" . "\\subsubsection*{%s}"))
     ("exam" "\\documentclass[12pt, addpoints, answers]{exam}"
      ("\\begin{questions}%%%s" "\\end{questions}" "\\begin{questions}%%%s" "\\end{questions}")
      ("\\titledquestion{%s}" . "")
      ("\\begin{parts}%%%s" "\\end{parts}" "\\begin{parts}%%%s" "\\end{parts}")
      ("\\part[%s] " . "")
      ("\\begin{subparts}%%%s" "\\end{subparts}" "\\begin{subparts}%%%s" "\\end{subparts}")
      ("\\subpart[%s] " . "")
      ("\\begin{solution}[%s]" "\\end{solution}" "\\begin{solution}[%s]" "\\end{solution}"))))


But heck, this is what custom is for!

If I don't figure it out I will send a bug report.