How to handle button states in a toolbar

I'm working on a toolbar containing objects that can be dragged into documents. You can also click on these objects to add them to the document. Some of these objects have restrictions and can be added just once. We show tooltips while hovering the objects that show these restrictions. The app manages many documents and you can browse them while the toolbar stays fixed on the right side of the window.

Once you added the object with restrictions (Blue button), is it better to disable it in the toolbar and show a tooltip on hover (picture A) or to keep the object active and show a message when you try to use it again (picture B)?