I believe this is due to the new syntax change for export blocks
announced a bit back. See:
- http://orgmode.org/cgit.cgi/org-mode.git/plain/etc/ORG-NEWS
Try this instead:
* Hello
#+BEGIN_export latex
hi I am latex
#+END_export
I was going to say the same but then I saw that Andrea is using an org-plus-contrib version. The new syntax would go in effect in org 9.0 or for someone using org built from the master branch.
It should not affect users using org from maint branch or org/org-plus-contrib from Org Elpa.