Oh, it could be so easy. Should have post this much earlier. THANK YOU! So, what is /root/.my.cnf for? Can this probably checked within update process?
When starting the regular update from 1.4.3, I got the following DB-error 1045. All passwords were correct. Reconfiguring and other tricks didn't work. Also my supporter thinks, that this is caused by the software. Does anyone know, how to fix?