Scratch what I just said, Daniel. I was unable to repro what you were experiencing until I put iTween into another folder - so what’s causing your errors is most likely from not placing it in the same folder I did.
It’s my fault for only suggesting Content\Blueprints\iTween. It really should be exactly that. Yor content browser should look like this:
The relative paths still keep, you just need to make sure your relative paths are the same as mine.
Do people still use the Blueprints folder? Should I move everything to the root folder?