Baking trouble using a cage I have created a high poly model of a castle wall and I would like to save on rendering time by baking the detail to a low poly counterpart. 

I followed this Tutorial : https://bit.ly/2Iy3WF7

However when I come to bake I get an error message saying the following : Invalid cage object, the cage mesh must have the same number of faces as the active object. 

I'm assuming the active object is the low poly mesh. But in the image example you can clearly see that they do have the same number of faces. is this a bug or have I done something wrong.
When selecting the active object use the Ctrl + Click instead of Shift + Click.