You will see this message when:
You have completed your Personal Educator Account trial or selected "Buy Now" and you do not have any student accounts set up.
or
You started with a Personal Educator Account, accepted an organization invite as an Admin or Educator, and you removed all your students from the Personal Educator Account. The Personal Educator Account is still "Active", until that current months subscription runs out. When the subscription runs out you will be able to access the tool with your Educator/Admin account.