It looks like your Postgress installation is a bit broken. How did you install it (from RPMS, compiled from the source)? Did you install it over older version of Postgress? Did you make any configuration changes? What OS/Postgress version are you running?
Trying to make work sth. that is broken is usally more difficult than starting over so your best bet could be just removing Postgress and re-installing it from scratch. I myself don't know almost anything about Postgress yet I've installed it succesfully a few times from RPMS (rpm -ihv postgress*.rpm). It takes care of everything.
