If you have PostgreSQL 8.x you need to set the compatibility flags in postgresql.conf.
https://openacs.org/xowiki/How_to_install_in_Postgres_8.x
After you make sure you have those settings correct, restart PostgreSQL and then try to install again after removing and recreating the datbase.
If you still have a problem go back in the error log to the first error that occurs during the install and post that to the forums.