Indeed what @cib is saying solves my problem.
Just modify the file plugins.sbt
in my projet directory.
Change the line :
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.4.2")
to:
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.3.9")
and you'll not get any errors doing activator run
again.