Can I re-invite a Customer Portal user?
Yes, you can re-invite your Customer Portal user if they have not accepted their first invite.
To re-invite a user, Goto Setup>Customer Portal>Users
In the Customer Portal Users page, you can find the list of portal users and their confirmation status. A portal user who had not accepted the invitation would be listed as Not Confirmed under the Confirmation Status. Choose the user by clicking the check box in the front of their Name and click Re-Invite to resend the Customer Portal invitation.