Error after upgrading nginx

[mawan]

By using root account, I type apt-get upgrade to upgrade nginx.
After this, all my websites are not working. Error message is:

500
Internal Server Error
Sorry, something went wrong :(

How to resolve this?
I use Ubuntu 16.04.1 LTE and latest VestaCP.
VPS on Digital Ocean.

[skurudo]

Please add a little more info:

> Installed Software (what you got with the installer):
Type here, e.g. php-fpm, apache, nginx, mysql

> Steps to Reproduce:
Type here, e.g. install vesta and type cat /etc/issue

> Related Issues/Forum Threads:
Found anything that might be related to this? It might help us find the cause.

> Other Notes:
Anything else? May be logs?