Classic error with SmartView. The problem is that a user's last refreshed point of view is stored in the tables. This is a double edged sword (nice part is it's efficient/downside is it breaks sometimes).
The solution to this issue is to remote into the SQL database behind HFM. Expand "Databases" -> HYPHFM (or the like) -> Tables -> Find your application_USERPARAMS -> right click and edit top 200 rows. Find that users "USERMBRSEL" and delete the record.
This should reset the stored point of view and allow the user to continue per normal.
The way to confirm my diagnosis is correct is to test whether this user can access another application with his smartview, as this error is application specific.
Thank you everyone for your answers - we really appreciate it! As it turns out, Hyp201207's solution was spot-on. We executed the following steps:
1. Made a full backup of the database before attempting any direct changes in HFM repository.
2. Ran the following query to reset the user's POV:
DELETE FROM <appname>_USERPARAMS WHERE Username like '<username>@%' and Parameterkey = 'UserMbrSel'
< appname> = (The company's HFM App name)
<username> = (The affected user's User ID)
3. Requested the user to login to Smart View and verify that he could connect - at which point in time he was successfully able to do so.