first, i hate phpbb. mailing lists work much better. but anyway...
i apparently registered here several months back. i forgot my username. since the "forgot your password" section requires a username, i just decided to start a new account. however when i clicked to finish the registration it complained about my email address - firstname.lastname@example.org. there was already an account with that email address associated with it.
the forgot your password section doesn't accept an email address for the member name.
so i have a few other email addresses, so i used one of those. but it seems like a simple thing to search for the email address on the "forgot your password" section.