PBSPro uses pgsql to store the server configuration, and comes with a pgsql embedded (see rpm -ql pbspro-server). You will need to create a new system-level user, typically called ‘pbsdata’, and ensure that /var/spool/pbs/datastore is owned by that user. The RPM does not automatically create that user, which is not obvious, in my opinion. I would do this on a new PBSPro install:
groupadd pbsdata
useradd -g pbsdata -r pbsdata
mkdir -p /var/spool/pbs/datastore
chown pbsdata:pbsdata /var/spool/pbs/datastore
Then start PBS server.