This means that your school has signed up for school or district features on Edmodo and you are logging in through the school or district's network. However, you have not yet joined a class/group that is owned by a teacher who is in your school's network.
To resolve this, please enter your teachers' Group Code. If they are part of the school or district network, then you will be able to log in. If the teacher who owns the class/group has not yet joined the network, then please have the teacher join the network. Once they do, you will be able to log in.