If you are using Oracle Single Sign On (11.1) then this can be caused if the APPS DN password has expired in OID.
You can check whether this is the cause by manually creating a user via the E-Business Suite 'User' form. If the above is the cause you will receive the following error:
"Unable to call fnd_ldap_wrapper.create_user due to the following reason:
ORA-20001 - The LDAP APPS DN **orclapplicationcommonname=xxx,cn=ebusiness,cn=products,cn=oraclecontext,dc=xxxxx,dc=co,dc=uk** password has expired.
Please contact the Administrator to change APPS DN password.."
The solution is to remove the expiration of the password for this user in OID.