Since Tails 3.0 has been released recently and many people have been having issues with installing it on different USB flashes, I thought I will let you guys know the easiest solution to the problem.
Problem: "Your USB flash name" is configured as non-removable by its manufacturer and Tails will fail to start on it. Please try installing on a different model.
Solution:
Boot up tails and set an admin password
Run this command in the terminal:
sudo perl -pi -E 's,media_removable,removable,' /usr/lib/python2.7/dist-packages/tails_installer/creator.py
This should solve your problem and now Tails should allow you to install on your USB flash