I was getting an error
Mono.Cecil.AssemblyResolutionException: Failed to resolve assembly: 'UnityEngine.UI, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'
caused when loading DOTween46.dll. I'm using Unity 5.2. I don't know why it would complain about that, but using the raw source files for DOTween did fix that error. The DLLs are included in the git repo.