Integrate custom plugin with WHM default theme?

Question: How can i integrate default whm theme (x) with custom whm plugin UI. I have tried following the guidance on 1)whm plugin - interface 2)create a new whm interface in template toolkit When i run script index.cgi it gives me " Internal Server Error 500 No response from subprocess (/usr/local/cpanel/whostmgr/docroot/cgi/watch7/index.cgi): The subprocess reported error number 72,057,594,037,927,935 when it ended. The process dumped a core file. cpsrvd Server at vps235171.example.com" ->main.tmpl is using default script provided on $template_file }, ); } # my $URL; # if ( 'root' eq $ENV{'REMOTE_USER'} ){ # $URL = "../cgi/watch7/index.php"; # }else{ # $URL = "../cgi/watch7/index.cgi"; # } # print "Location: $URL\n\n";