Unexpected error

Please suggest when do we get Unexpected error message (Dynamics CRM 2013 , on-premise)

One of the user when trying to navigate  Service area ----- >subarea(eg report ), is getting Unexpected error message and is unable to view subarea , while other sub areas are working fine for user's role . I tried using system admin role and was able to access Service area---> subarea , without any error. 

Doesn't seems like security role issue however unable to understand why only one area is throwing error for user's role.

Any comments/help is much appreciated. 

Thanks,

Hanna