If(defined $data->{articleResponse}->{NOTICE}->{COMMENT}->{LR}->{REJECT_INFO}){

     If(defined $data->{articleResponse}->{NOTICE}->{COMMENT}->{LR}->{REJECT_INFO}->{ERROR_REJECT_CODE}){

        $rejCTag = $data->{articleResponse}->{NOTICE}->{COMMENT}->{LR}->{REJECT_INFO}->{ERROR_REJECT_CODE};
        }
     If(defined $data->{articleResponse}->{NOTICE}->{COMMENT}->{LR}->{REJECT_INFO}->{REJECT_INFO_DESK}){

        $rejDTag = $data->{articleResponse}->{NOTICE}->{COMMENT}->{LR}->{REJECT_INFO}->{REJECT_INFO_DESK};
        }
   }

Here is a link to for XML-Simple interface just an fyi.

http://search.cpan.org/dist/XML-Simple/lib/XML/Simple.pm

http://search.cpan.org/dist/XML-Simple/lib/XML/Simple.pm

I've encounter syntax errors along the if statements, please let me know what should i do.

what you should do is ditch Perl for a real programming language like Ruby, Java, or C# ;)

But as it is, the error sounds a lot like you have a typo somewhere in your code.