Error:

SQL Server Setup could not connect to the database service for server configuration. The error was: [Microsoft][SQL Native Client][SQL Server]Login failed for user ‘sa’. Refer to server error logs and setup logs for more information. For details on how to view setup logs, see “How to View Setup Log Files” in SQL Server Books Online.

Error Message:

Causes:

1. Due to improper SQL uninstallations, SQL Native client provider might be corrupted.
2. This error seems to be linked to missing or incorrect registry entries. Uninstall everything related to SQL that might be on your computer.
3. Logged on user may not be an administrator. Administrator privileges is required to install SQL Server.
4. Due to improper SQL uninstallations, your registry is not clean and might be corrupted.
5. Disable password policy.

Workaround 1:

Make sure that you are running the SQL Server setup as “Run as Administrator”.

Workaround 2:

When you are at the point of the failure, do not cancel the installation,

Run this registry SqlNativeClientRegistryConfiguration.reg

Download: SqlNativeClientRegistryConfiguration

Workaround 3:

Remove SQL Server 2005 completely from Control panel

Control Panel | Add or Remove Programs | Microsoft SQL Server 2005

In the first dialog, make sure to select the “RELYONDB: Database Engine” radio button.

If RELYONDB is the only instance, then select all check boxes & Click Next and Finish to proceed with the uninstall.

If there is no other SQL instance, I would go on to clean out all SQL components with the following steps.

Uninstall Microsoft SQL Server Native client

Uninstall Microsoft SQL Server Setup support files

Uninstall Microsoft SQL Server VSS writer