I've done quite a few SQL Server 2008 cluster installations before which is why this struck me as a surprise. I was trying to rebuild one of my test mahines when I hit upon this error message while adding the second node on a two-node SQL Server 2008 cluster on a Windows Server 2008.
The current SKU is invalid.
After a quick search on the Internet, I found out that this is a bug (my first time to get bitten by it). There is currently a Microsoft Connect item regarding this and it mentions having Cumulative Update 1 applied should fix this issue but I wouldn't want to apply a hotfix for something like this as I normally do that after the entire installation is complete. A few more hits on Google directed me to a forum post that mentions about deleting the DefaultSetup.ini file from the installation media. Just make sure you copy the installation key from this file before deleting it or simply do what I did - move the file some place else. What I usually do is copy everything on a local disk for the installation to be a lot faster. After going thru the Add node to a SQL Server failover cluster option, I manually entered the installation key and it the installation completed successfully. I wonder why I never got this error during my previous installations