Steam decided to force update my 9.7 to 12. Ver. 12 on my PC is causing hang ups and lag. Just like ver. 10.
When i run the installer over the top of 12, it does install, then throw a key error.

How do i revert back to 9.7 with my Steam Key ?

This is the error when installing 9.7 over Steam 12.
Keith was able to provide a work around.
Thank you for your help.

How can solve this? My Steam code is still not working in the old version.