Private key to connect to the machine via SSH must be owned by the user running Vagrant

The error message is clear and suggests a solution. You need to set ownership to the private_key to the current user.

In the normal situation the following command should be enough:

sudo chown `whoami` /media/bcc/Other/Linux/vagrant3/.vagrant/machines/default/virtualbox/private_key

However in your case it is likely (because of /media) that you have placed your project on an external disk. If you use a filesystem that does not support permissions, then either you have to check

ls -l /media/bcc/Other/Linux/vagrant3/.vagrant/machines/default/virtualbox/private_key

and run vagrant up as the user listed as the file owner or move your project elsewhere and assign permissions properly.