It looks like Gesture Recognizer probably defines a Strings class in the global namespace. I don't own Gesture Recognizer to double check.
I would contact the author of Gesture Recognizer and ask if he uses namespaces in his asset to avoid collisions with other assets.
A workaround is to open FsmComponentInspector.cs and replace "Strings." with "HutongGames.PlayMakerEditor.Strings." If you then get errors in other scripts you will need to do the same to those.
EDIT: I've attached a unitypackage with the above workaround applied. NOTE, this is a temporary fix that will get overwritten when you update. The real solution is for Gesture Recognizer to use namespaces.