OK, I worked it out. After looking at the source code for SendPassword.ascx.cs, it was pretty obvious that the most likely cause is that RequiresUniqueEmail was set to false in my MembershipProvider config. Logged in to server and checked web.config, and sure enough that was the problem.

Somehow, even though my site is set up to use email addresses as logins, they weren't set as unique.

Anyway, changed it to true and now self service is working again.

Dylan

Well, we were using Usernames, and I couldn't set the site to use email addresses for logins until I had removed all the duplicate email addresses, so I kind of assumed that the setting was part of the changeover.

Obviously not, as I checked today and there were already new duplicate email addresses in the system, with people who forgot their password setting up a new account with the same email address as the old account.

Anyway, should be good now.