[O] orgmode beamer mode: BMCO does not export to latex any longer

[Martin Steffen]

Hi, 

since recently I have a problem with exporting org-beamer-mode, the
culprit presumably

                 BMCOL

It's org, in beamer mode. The mode still allows to turn some headers
into BMCOL (multiple colums) via some keybindings

        ``C-c C-b |'' (representing org-beamer-select-environment "|")

That results in lines like
----------------------------------------------------------------------------------
*** Some text                                                 :B_block:BMCOL:
    :PROPERTIES:
    :BEAMER_col: 0.5
    :END:
.................................................................................

which is supposed to  be a block taking 50% of the slide's width.


So far so good (and as it used to be). 

Now, when /exporting/ the org-document to latex with 

         C-c C-e l b (l for latex, b for beamer-class)

the export peocedure trips over some error and 
              
               nothing is exported 

(the same occurs if I directly want to generated the PDF, and also if I
export the beamer-org document to a ``arcticle''-kind of style, so to
have a script). The message for the error reads like


------------------------------------------------------------------------------
[...]
org-babel-exp process tac at position 108835...
org-babel-exp process tac at position 109478...
org-beamer--format-block: Wrong type argument: number-or-marker-p, nil
-----------------------------------------------------------------------------


It seems that the BMCOL is the culprit, org-beamer still export a
complicated and long document (as it did before), but probably a recent
update made it stumble over that particular element.


Any suggestion where to look?

thanks, Martin

PS: org-version="9.1.6"
    emacs-version: GNU Emacs 24.3.1