When trying to install additional features to an existing SQL 2008 R2 installation you can get.
Error Message:
SQL Server Setup has encountered the following error: The SQL Server product key is not valiad. To Proceed, re-enter the product key values from the Certificate of Authenticity (COA) or SQL Server packaging Error code 0x84B40000
Solution:
Find DefaultSetup.ini on the installation media Remove any product key found in PID
;SQLSERVER2008 Configuration File
[SQLSERVER2008]
PID=””