APEX

Dear All,

i am using apex 4.2 with latest apex listner,oracle database 11g R2 64 bit, windows 7, internet explorer 9.

i want to configure ldap authintication.

i am following the following blog

http://ruepprich.wordpress.com/2012/11/02/ldap-authentication-with-apex/

i am stuck with the following line

i have created the same trigger like below

DECLARE 
 l_acl VARCHAR2(100) := 'ldapacl2.xml'; 
 l_desc VARCHAR2(100) := 'LDAP Authentication for ldap.hctsrvpdc01.hct.org'; 
 l_principal VARCHAR2(30) := 'APEX_040100'; -- upper case 
 l_host VARCHAR2(100) := 'ldap.hctsrvpdc01.hct.org';
BEGIN -- Create the new ACL. -- Also, provide one starter privilege, granting the schema the privilege to connect. 
 dbms_network_acl_admin.create_acl(l_acl, l_desc, l_principal, TRUE, 'connect');  
 -- Now grant privilege to resolve DNS names.  
dbms_network_acl_admin.add_privilege(l_acl, l_principal, TRUE, 'resolve');  
 -- Specify which hosts this ACL applies to. 
 dbms_network_acl_admin.assign_acl(l_acl, l_host);  
COMMIT;
END;

but when i run it from sysdba, it give the following error

ERROR at line 1:
ORA-44416: Invalid ACL: Unresolved principal 'APEX_040100'
ORA-06512: at "SYS.DBMS_NETWORK_ACL_ADMIN", line 252
ORA-06512: at line 7

how to fix this issue? what is the   l_principal VARCHAR2(30) := 'APEX_040100';??? how could i sure it is  APEX_040100?

Regards.