[O] org-plus-contrib fails to compile

[Glyn Millington]

Good morning list!

Emacs 25.3.1 on Linux

For many upgrades now (over the last year or so) when I have tried 
to upgrade org-plus-contrib with the package management system 
pointed at the Org repository, the package is installed but 
compilation fails with a massive (23.6MB!) backtrace  which begins 
like this:


Debugger entered--Lisp error: (void-variable This) 
 eval-buffer(#<buffer  *load*> nil 
 "/home/glyn/.emacs.d/elpa/org-plus-contrib-20180430/org" nil t) 
 ; Reading at buffer position 5 
 load-with-code-conversion("/home/glyn/.emacs.d/elpa/org-plus-contrib-20180430/org" 
 "/home/glyn/.emacs.d/elpa/org-plus-contrib-20180430/org" nil t) 

None of the lisp files in the package are compiled.

Can anyone point me to likely sources of the problem (my own 
cluelessness goes without saying! ) ?

with thanks


Glyn