First workaround, Cluster Validation was good but SQL installer still complained
https://support.microsoft.com/en-ca/help/953748/error-message-when-you-install-sql-server-2008-on-a-windows-server-200
Setup /SkipRules=Cluster_VerifyForErrors /Action=AddNode
Second Workaround is actuall a MS Bug, where I had to comment out the pre-saved license key in the installer folder and entered it manually instead
https://digitaljive.wordpress.com/2009/06/22/%E2%80%9Cthe-current-sku-is-invalid%E2%80%9D-when-adding-second-node-to-sql-2008-cluster/
https://support.microsoft.com/en-nz/help/957459/fix-error-message-when-you-try-to-add-a-second-node-to-a-sql-server-20
Basically go to \x64 folder and modify the Defaultsetup.ini file to comment out the serial number (and paste it in during install)
;SQLSERVER2008 Configuration File[SQLSERVER2008];PID="XXXXXXXXXXXXX"
