Hi Scarlet,
Thank you for using our service. To trouble shoot the problem, please forward the share notification email to DriveHQ customer support.
Otherwise, to solve the problem, you can ask the other person to share the folder again to your DriveHQ username. When sharing a folder, the person can either enter email addresses, or more easily enter DriveHQ usernames. (Contact groups and sub-group can also be entered).
If a user has already shared a folder before, he/she can use "Manage My Share" feature to edit an existing Share. He/she can also share the same folder again using a different Share Name.