Why while starting iptables service following error is thrown "Applying iptables firewall rules: iptables-restore: line X failed" ?

Issue

• Some customer iptables rules are configured in the file. While restarting the iptables services, getting error as iptables-restore: line X failed [FAILED]
• Iptables service is not getting started and throwing error as below:

root@HOSTNAME ~]# service iptables stop
Flushing firewall rules:                                   [  OK  ]
Setting chains to policy ACCEPT: filter                    [  OK  ]
Unloading iptables modules:                                [  OK  ]
[root@HOSTNAME ~]# service iptables start
Applying iptables firewall rules: iptables-restore: line X failed
                                                           [FAILED]
[root@HOSTNAME ~]#