I'm glad you figured out the animation issue with your chest.
We use an avatar for the chest because we animated the chest outside of Unity. If you animate it within Unity you won't need one. Since it is a simple hinge rotation animating it in Unity makes perfect sense.
As for the error you are getting.
"The Item Description has a category attribute box set ...."
Essentially this means you have a component (the Item Description) which is referencing item categories from another database (the demo database most likely).
So go find your ItemDescription component within the chest menu and remove (or replace) the Category attribute box set. Most likely the currency UI within the description is also pointing to the wrong database so make sure to change that too.
In the future I will look into a solution such that if a similar category already exist in the loaded database it'll use that category instead of the one set in the inspector, it'll avoid errors like the ones you have.