You know, I’ve never actually built a game in UE4 using the plugin version of iTween, I always install the source version, so I may have overlooked something!
When you install iTween, it’s supposed to update your project’s Build.cs for you with all of the necessary dependencies. It may be possible that when installing the plugin version this step does not occur, though it shouldn’t work in the editor if that were the case. I’m out of town today, but tomorrow I will be in-office and will get to the bottom of this by doing some testing and get back to you with a solution asap.