Revit generates an error (shown below) when initializing/updating a project for use with ElumTools. This type of error can occur with any Revit Addin which makes use of the Revit API's extensible storage functionality. At the time of writing, Autodesk has been contacted by Lighting Analysts and has confirmed they do not know how to solve the problem (apart from the steps listed below).
1. Close all running instances of Revit
2. Open the file in question in a new Revit instance.
3. Immediately initialize ElumTools, if it has not been initialized previously.