Hi Nikos
I'm afraid I cannot help you much since I'm not working with a Bavelloni machine anymore. But it might be that there was a tool still present in the spindle before you changed the motherboard, so I think you might need to find a way to reset the tool store so there is no tool selected.
You might be better of to email Bavelloni directly the error code you get, they will be better able to help you.