Yesterday, during a tentative to install SP1 on customer farm, I received a really stressfull failure message (below record on Upgrade.log):

========================================================================

[PSCONFIG] [SPManager] [INFO]
[8/22/2011 7:38:18 PM]: Upgrade Boot Strap starts. Initialized in Mode:
InPlace, as MachineAdmin: True.

[PSCONFIG] [SPManager] [DEBUG] [8/22/2011 7:38:18 PM]: Detected v4 configuration database dsn: Data
Source='"ColSQL08Web                  "';Initial Catalog=SharePoint_Config;Integrated Security=True;Connect
Timeout=15;Application Name="Microsoft SharePoint Foundation".

[PSCONFIG] [SPManager] [ERROR] [8/22/2011 7:38:32 PM]: SPManager.Initialize failed.

[PSCONFIG] [SPManager] [ERROR] [8/22/2011 7:38:32 PM]: Exception: A network-related or instance-specific error
occurred while establishing a connection to SQL Server. The server was not
found or was not accessible. Verify that the instance name is correct and that
SQL Server is configured to allow remote connections. (provider: Named Pipes
Provider, error: 40 - Could not open a connection to SQL Server)

[PSCONFIG] [SPManager] [ERROR] [8/22/2011 7:38:32 PM]:    at
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception,
Boolean breakConnection)

=====================================================================

After that has been verify that SQL Connection was OK, that all SQL Services was started and that Windows Firewall was stopped, I was disappointed discovering that there was not solution other than remove this server from farm (this was just a test environment with three server).

Reading again Upgrade.log I noticed that Data Source name was strange, with "apexes" and a lot of blank space: now I knew because my Config_DB was dissappear!!!!!!!

I changed on Registry the correct key dsn [pay attention: this was a test environment!!!!] Computer\HKEY_LOCAL_MACHINE\Software\Microsoft\Shared Tool\Web Server Extensions\14.0\Secure\ConfigDB