>>> "Eric" == Eric S Fraga <esflists@gmail.com> writes:

   > On Sunday, 16 Dec 2018 at 19:16, Uwe Brauer wrote:
   >>>>> "Eric" == Eric S Fraga <esflists@gmail.com> writes:
   >> 
   >> > Can you be explicit about how you are exporting to beamer 
   >> 
   >> Either 
   >> 
   >> C-c C-e l l
   >> 
   >> Or 
   >> 
   >> C-c C-e l o

   > And here is the problem.  These are not the export directives to use for
   > beamer.  Use C-c C-e l b to generate beamer LaTeX code or C-c C-e l O to
   > open the PDF.

Sorry misprint.

I meant C-c C-e l b

Which does not work. 

The problem is problem with custom, I thought the logic would be like this.

    1. Emacs is started,

    2. The customization is loaded, which in my case is 

(custom-set-variables
 '(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}"))))

Then (require 'ox-beamer) should via add-to-list, add beamer but somehow
it does not. I would call this a bug, but Tim said Emacs changed its way
of initialization and this could be the result. In any case I will send
a bug report, maybe a developer will say something.

Uwe