Thank you for your reply. I've tried what you suggest:
1. New browser session, go to "guest_register.php?_clear=1"
2. Lookup sponsor, input other details and submit form.
3. Sponsor gets e-mail, clicks link and approves.
4. Receipt page ("guest_register_receipt.php?refresh=1") auto-refreshes and login button becomes available.
5. Click login button.
6. SAME ERROR: -:NwaLdapSponsorUserSearchAjax not callable
Am I doing something wrong?