I'm running CiviCRM 4.7.10 and Drupal 7.50.
I have had a Civi database for a while, but am now wanting to give people front end accounts in order to use some features there.
My problem is that when a user, who is already a contact in Civi, tries to create a Drupal account, they get the rather unceremonious "DB error: already exists".
I'm confused because I keep reading that Civi is set up to automatically merge new users with existing contacts on matching emails (or whatever criteria is set in the Unsupervised deduping settings for Individuals - mine is using email only at the moment).
I would love to understand how this is supposed to work and how to fix it when it doesn't.