The problem isn't really generic as my title says...
I've worked on Kohana site on local, and just put it online on ovh server. This site is under a subdomain. My connexion to mysql seems to be ok.
It can't find my models ! But I can display my views ! And it worked perfectly on my local.
I don't know which way I have to take to find my solution...
[EDIT]
I use the function Kohana::find_file() to try to find the path of my model > nothing. But it works for my views.