[otrs] Ldap integration

Hi all, my name's Paolo and i work for a company where i try to configure ldap-authentication for windows server 2003. I installed on a linux debian OTRS, i followed indication on a OTRS site but, when i change the Config.pm file, i try to restart apache service I received this error message: [error] Global symbol "$Self" requires explicit package name at /opt/otrs//Kernel/Config.pm line 121. the 121 line is the following: $Self->{'AuthModule'} = 'Kernel::System::Auth::LDAP'; Error is the same for all lines into the Config.pm file. Can you help me about a solution of this error, for me is very important because for this error i can't use OTRS. Thank you in advanced. Best regards Paolo