Hi I find the error

In /etc/httpd/conf.d/otrs.conf it was missing the yellow line just below :

<Location /otrs>

#  ErrorDocument 403 /otrs/customer.pl

  ErrorDocument 403 /otrs/index.pl

  SetHandler  perl-script

  PerlHandler ModPerl::Registry

  Options +ExecCGI

  PerlOptions +ParseHeaders

  order allow,deny

  allow from all

</Location>

bizarre !!