after upgrading 4.0 to 4.2 some LDAP apps work and some dont..
APEX_LDAP.is_member is not used so bug #15836959 is not an issue.. tried it anyway, didnt help..
figured out if I edit the LDAP Authentication Scheme, without making any changes and click Apply Changes..
then it starts working again...
This is weird.. Least its an easy fix