Hi,
If its happening for a single user only i would suggest you to do the following:
1. Suggest the user to browse to the PCA page using the following:
https://10.106.117.133/ciscopca
Please note that user will have to use the web application password to be able to login. If user is not sure about the web application password then you can change the web application password on the unity and have them login.
CUC >>> Users >>> password settings >>> Select web application
2. Download all the saved/important messages.
3. Once he has the backup of the saved messages, delete the user from CUC which will basically delete the mailbox of the user and create it again.
Aseem