I have updated my Zenphoto script and now have an error.

Zenphoto encountered an error
MySQL Error: Zenphoto received the error Access denied for user 'magija_znp01'@'localhost' (using password: YES) when connecting to the database server.

I checked my zp-config.php file, and found out that all info is missing:

$conf['mysql_user'] = "";
$conf['mysql_pass'] = "";
$conf['mysql_host'] = "localhost"; // Won't need to change this 90% of the time.
$conf['mysql_database'] = "";

I have updated zp-config.php with valid user name and password, but the error was still there. I then deleted the user and added the new one, but the error remain there.

What should I do?

There is a mismatch between what your error message shows and what you say is in your zp-config.php file. This makes me think maybe you are updating the wrong file.

Is the user name in the error message correct? If so maybe somehting has changed on the server. If not you need to find the zp-config.php file that contains that user name.

BTW, from what version to what version did you upgrade?