Forum OpenACS Development: Re: Error installing 5.9 from scratch
The install script install-oacs.sh  creates among other things the oacs_user with the configured value in postgres and alters the default db_user that value (normally "nsadmin"). This happens in nstall-oacs.sh around line 310. So, an explanation might be, that install-oacs.sh was not run (has not tailored the startup file) or stopped prematurely.
Thank you again