"Error: That IP address can't be assigned-to" when running app

Use:

python manage.py runserver 0:8000

You should check with your IP, as mine was changed and was getting the same error

It is equivalent to error code #99 in c language errors list, It's described by this term:

Cannot assign requested address

It is not a permission problem, because permission's error code is different so I think it's because you have not that IP address set on your computer. When you try to run server on an specified IP address, you should have it set on one of your network interfaces.

Simply the IP address you're trying to run server on it is not your current IP address.