We don't permit two accounts to share an email address; there are enough free email providers out there that no two users should have to share. See http://pkp.sfu.ca/support/forum/viewtopic.php?t=1647
for some discussion on how to find a user who doesn't appear on the "All Users" list -- briefly, that list only shows users who have a role in the journal, and you may need to give them one (e.g. Reader) before they'll appear. Use the "Enroll Existing User" link at the bottom of the "All Users" page, choose a role (e.g. Reader), and enroll them.
Open Journal Systems Team
Don't miss the First International PKP Scholarly Publishing Conference
July 11 - 13, 2007, Vancouver, BC, Canada