In place upgrade from SQL Server 2000 to SQL Server 2005 may fail with the following error message though SQL Server 2000 instance may be at the build 8.0.2039 (SP4)
Name: Microsoft SQL Server 2000
Reason: Your upgrade is blocked. For more information about upgrade support, see the "Version and Edition Upgrades" and "Hardware and Software Requirements" topics in SQL Server 2005 Setup Help or SQL Server 2005 Books Online.
Service pack requirement check:
Your upgrade is blocked because of service pack requirements. To proceed, apply the required service pack and then rerun SQL Server Setup. For more information about upgrade support, see the Version and Edition Upgrades topic in SQL Server 2005 Setup Help or SQL Server 2005 Books Online.
You can double check that the file version of SQLSERVR.EXE is equal to or greater than 8.0.2039 and the SQL Error logs also reports the build number as 8.0.2039 or above it.
Add the following keys in the registry at [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer\MSSQLServer\CurrentVersion] if you don’t find them and then do the upgrade.
Name: CSDVersionNumber Type:REG_DWORD Data:400
Name: CSDVersion Type:REG_SZ Date:8.00.2039
Note: If have installed 32 Bit SQL on a 64 bit box check the above keys at the following location [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\MSSQLServer\MSSQLServer\CurrentVersion]
IMPORTANT : This resolution contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:
256986 Description of the Microsoft Windows Registry
SE, Microsoft SQL Server.
TL, Microsoft SQL Server