I tried to upgrade modx 2.5.4 to 2.5.7 when I got the ERROR

MODX Setup cannot continue.

Unfortunatly the Problem was very simple, the directory: /var/lib/php/session/ was not writable by the php User (in my case nginx) :( once i figured that out I could fix the problem very simple

chmod -R nginx:nginx /var/lib/php/session/

DONE!