I'm sorry, I don't understand the question. What is it doing? What do you want it to do instead?
when I use the Unified Camera tool, I might be able to change the viewpoint using the mouse, but there comes an error tone and I can not use unified camera tool, it is blocked.
Did you add a camera to your composition? The unified camera tool will not work without a camera in the composition when your view is set to Active Camera. The unified camera tool will work with custom views but this will not give you a view that you can render. Custom Views are only for assistance in setting up your scene. Only the active camera will render.
I hope this helps you out.