SQL Server 2005 Installation SKUUPGRADE=1

When installing SQL Server 2005,  I encountered an "Edition Change Check (Warning)". Detaied as below:

"To change an existing instance of Microsoft SQL Server 2005 to a different edition of SQL Server 2005, you must run SQL Server 2005 Setup from the command prompt and include the SKUUPGRADE=1 parameter."

Someone says it's due to conflict between SQL Server 2005 and Visual Studio 200X. I'm not sure. But the work around is:

1. In commond prompt, go to "Servers" directory under SQL Server 2005.
2. run "setup SKUUPGRADE=1". Make sure it's capital. Otherwise it won't work for some reason.