If Afghanistan, China, Mexico or Persia become allies to either side there is a problem as the corresponding activation file is missing. The AI goes into an infinite thinking loop during the Political Phase.
Calvinus was able to solve my problem and asked if I would post the solution on the forum. If I have done it correctly the attached link should give you four files, afg.ini, chi.ini, mex.ini and per.ini.
These files need to be dropped into:
World War One\Data\AI\Modding.
http://www.mediafire.com/?sharekey=38ce76db63742b7fd2db6fb9a8902bda