In the Unity Editor menu, if you go to Edit > Project Settings > Services > Mediation or Services > Mediation > Configure to open the Mediation Adapter Configuration to attempt to install or uninstall an adapter, the UI may become unresponsive. This is potentially due to a corrupt file (which can occur when upgrading from 0.1 to 0.2).
To fix this, delete the file Assets/Editor/MediationAdapterDependencies.xml and try to build. Afterward, go back to the Adapter Configuration screen and you should be able to install/uninstall again.
For more information, see documentation on Unity Mediation.