ISAPI filter with LDAP over SSL only works as administrator

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http://serverfault.com – I have created an ISAPI filter for IIS 6.0 that tries to authenticate against Active directory using LDAP. The filter works fine when authenticating regularly over port 389, but when I try to use SSL, I always get the 0x51 Server Down error at the ldap_connect() call. Even skipping the connect call and using ldap_simple_bind_s() results in the same error. The weird thing is that if I change the app pool identity to the local admin account, then the filter works fine and LDAP over SSL is successful. I created an exe with the same code below and ran it on the server as admin and it works. (HowTos)