I should have mentioned that Autodiscover did work, and that EWS (https://email.clarion.edu/ews/exchange.asmx) test also passes. Just tested again, and as before when I click finish the dialog closes but no account is created.
UPDATE:
Just tried on my old laptop and it worked. Big difference is TB version - have TB38.5.1 on new laptop, TB38.2.0 on older.