[Owncloud] Problem with installation

[Vezzo]

Hi,
I have a setup of owncloud 4beta with lighttpd running without
problems on the local network.
Now I would like to access from the web, and I use nginx as a proxy,
but now I can't access, the server continues redirect me to the home
page with the credentials form, but if I install ownCloud 3 I have no
problem.
I can not find the problem, you know how can I do?
thank you very much

-- 
Francesco Vezzoli