Removed /usr/local/nagios/etc/usr/local/nagios/var directory and corresponding entry in nagios.cfg - nagios now able to start
Lowered shared_buffer value in /var/lib/pgsql/data/postgresql.conf from 32MB to 16MB and this got the XI interface going
Now the nagios process is not being detected as running even though it clearly is, and the active host/service check icons are intermittently blue. Waiting for reply from subashcbe.