How to use Reason 7 (Reason.app) on macOS Sierra
To add to the answer, the solution would appear to be found in the following link: 

https://www.propellerheads.se/support/user/reason/mac-troubleshooting/where-are-the-sound-banks-in-reason-9/

The folder in question in application support should be deleted in order for Reason 9 to launch. This should fix the issue.