Frédéric:
I'lml translete and send you a traduction of addon_pmail_notifymsg_eng.h
<wbr>tml
Could you rewrite this, please? I didn't understand this sentense.
You sent me the translation only of the language pack for the PM add-on (pmail_fre.php). I never received the translation of this template.
Whatever you have actually to do, is to create a copy of
templates/addon_pmail_notifymsg_eng.html, naming it as
templates/addon_pmail_notifymsg_fre.html and then translate it.
Now it seems you removed also the "_eng" version from the folder, but at least this file should be kept — if the program doesn't find the French version, it takes the English template.
If none is found, you'll get the error as described.