There were a lot of changes in this area in org-mode version 8.0. I believe
you updated from an older version 8.x version.

Here's info on the 8.0 upgrade: http://orgmode.org/worg/org-8.0.html

There are many backward incompatible changes in that version. So you should
read the above in full, especially if you are also using ox-latex and
ox-html.

The answer to your ox-beamer question is in the "Upgrading your setup"
section; you now need to explicitly require ox-beamer using one of the two
methods described there.
On Nov 6, 2015 12:51 AM, "童俊翔" <tongjunxiang@gmail.com> wrote:

I want to export org to beamer. It worked well previously when I press C-c
C-e l O. But in recent days, when I press C-c C-e l, the options for beamer
are missing. I can only export to pdf, not beamer.

What’s the problem, and what can I do?

Thanks a lot!