"Plugin Scala is incompatible with this installation" error with IntelliJ 14

On the link that you've provided you can see that compatible Intellij Idea builds for 1.7.4 version are 142.3553 — 143. The latest 14 Idea build has version lower than 142 - so it's incompatible with this plugin version. There is already EAP Intellij Idea 15 which you can download and install new scala plugin version on it.

I faced the same issue with 2020.2.4 Intellij IDEA. I just uninstalled the plugin and installed it again. Fixed the problem.