A missing first or last name value for the user causes this issue.  It is mandatory to enter the "First Name" field while creating an archive from the Arctera Management Console, however synchronizations of Cloudlink and/or Office 365 Sync allow archives to be created without both First & Last Name. This is because most mail platforms do not require both first and last name fields, and Arctera Unified Platform does require both. 

This generally happens with archives of shared mailboxes (mailboxes not tied to an Active Directory user). When such a user attempts to login, the above error is thrown. 

Login to Arctera Management Console and update the "First Name" field for the affected archive.

Users receive the following pop-up window when attempting to access Personal Archive (PA) portal: "Unable to login to Personal Archive with the error : Your account is not enabled for archive access. Please contact your Helpdesk for assistance." This happens despite being enabled for PA access.