Ref.
http://www.cisco.com/en/US/docs/voice_ip_comm/connection/7x/user/guide/assistant/7xcucugasst010.html
 
When I try to login Unity Connection Assistant Web Tool with Administration account, It show msg
"This user account does not have a mailbox and cannot sign in to the Cisco
Personal Communications Assistant. To use the Cisco PCA, you must have an
account with a mailbox."</td>

How to create username and password to login URL https://<unity_address>/ciscopca
 
Thanks,