Dear Bastien,
The error
> Wrong type argument: listp, t
was due to the following line
(add-hook 'org-mode-hook 'predictive-mode)
which was there in the .emacs file.
While predictive mode is on [without (add-hook 'org-mode-hook 'predictive-mode) in .emacs] in org-mode buffer, C-c C-e p produces an empty folder .predictive, in the folder where .org file is located. If I use (add-hook 'org-mode-hook 'predictive-mode) in .emacs then the generated .predictive folder contains all the .el and .elc files.
Thanks.
-----------------------------
Sanjib Sikder