The AcuXDBC DSN was set up with no password so users are prompted for the password when accessing the data.
Vision files were added via that DSN to an Access database as linked tables. That database was then queried using MS Excel but no password prompt was seen and the query failed with the 'connection failed' message.
There is no mechanism in AcuXDBC to manage the password prompt through multiple levels as seen in this example.
There are two solutions:
1. Add the password in the AcuXDBC DSN.
2. Query the AcuXDBC DSN directly from Excel rather than through the MS Access database links.