My SQL Server v6.5 (running on an NT v4.0 server) backups were running well
for months, then one day I started getting ACO4210E -- Failed to connect to
SQL server messages.  All my research failed to find the answer.

The problem was not ADSM, it was SQL Server / Windows NT.  After a reboot of
the NT server (which had been up for months) the problem went away.

Tivoli Storage Manager
Tivoli Data Protection for Microsoft SQL Server - Version 1, Release 1,
Level 2
(C) Copyright IBM Corporation 1997, 1999. All rights reserved.

TSM API Version 3, Release 7, Level 0
TSM Nodename: Something

License file exists and contains valid license data.

Logging on to the TSM server...

Logging on to the SQL server...

ACO4210E -- Failed to connect to SQL server.

sometimes ACO4210E is written as AC04210E