Unable to start/stop ns-slapd via systemd

Issue

Able to start/stop ns-slapd with " /usr/lib64/dirsrv/slapd-example-inst1/start-slapd" and "/usr/lib64/dirsrv/slapd-example-inst1/stop-slapd" but unable to start or stop ns-slapd via systemd:

#systemctl start dirsrv@slapd-example-inst1.service
Job for dirsrv@slapd-example-inst1.service failed because a configured resource limit was exceeded. See "systemctl status dirsrv@slapd-example-inst1.service" and "journalctl -xe" for details.

# journalctl -xe
Oct 06 12:10:03 tigger systemd[1]: Starting 389 Directory Server slapd-example-inst1....
-- Subject: Unit dirsrv@slapd-example-inst1.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit dirsrv@slapd-example-inst1.service has begun starting up.
Oct 06 12:10:04 tigger polkitd[716]: Unregistered Authentication Agent for unix-process:4013:6931 (system bus name :1.95, object path /org/freedeskto
Oct 06 12:10:11 tigger realmd[2953]: quitting realmd service after timeout
Oct 06 12:10:11 tigger realmd[2953]: stopping service
Oct 06 12:10:12 tigger fprintd[3814]: ** Message: No devices in use, exit
Oct 06 12:11:29 tigger spice-vdagent[3266]: primary: received release while not owning client clipboard
Oct 06 12:11:30 tigger spice-vdagent[3266]: clipboard: received release while not owning client clipboard
Oct 06 12:12:52 tigger polkitd[716]: Registered Authentication Agent for unix-process:4171:23841 (system bus name :1.96 [/usr/bin/pkttyagent --notify
Oct 06 12:12:52 tigger systemd[1]: Failed to load environment files: No such file or directory
Oct 06 12:12:52 tigger systemd[1]: dirsrv@slapd-example-inst1.service failed to run 'start' task: No such file or directory
Oct 06 12:12:52 tigger systemd[1]: Failed to start 389 Directory Server slapd-example-inst1..
-- Subject: Unit dirsrv@slapd-example-inst1.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit dirsrv@slapd-example-inst1.service has failed.
-- 
-- The result is failed.
Oct 06 12:12:52 tigger systemd[1]: dirsrv@slapd-example-inst1.service failed.
Oct 06 12:12:52 tigger systemd[1]: Starting 389 Directory Server slapd-example-inst1....
-- Subject: Unit dirsrv@slapd-example-inst1.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit dirsrv@slapd-example-inst1.service has begun starting up.
Oct 06 12:12:52 tigger polkitd[716]: Unregistered Authentication Agent for unix-process:4171:23841 (system bus name :1.96, object path /org/freedeskt
Oct 06 12:13:25 tigger dbus[658]: [system] Activating service name='com.redhat.SubscriptionManager' (using servicehelper)
Oct 06 12:13:25 tigger dbus-daemon[658]: dbus[658]: [system] Activating service name='com.redhat.SubscriptionManager' (using servicehelper)
Oct 06 12:13:25 tigger dbus[658]: [system] Successfully activated service 'com.redhat.SubscriptionManager'
Oct 06 12:13:25 tigger dbus-daemon[658]: dbus[658]: [system] Successfully activated service 'com.redhat.SubscriptionManager'
Oct 06 12:13:33 tigger chronyd[661]: Selected source 10.0.1.28