El error es el siguiente:
App Inventor was unable to find the App Inventor Setup command directory, which contains commands needed to connect to a device.
App Inventor suspects your Setup software is out of date.
When you press OK, App Inventor will start the Blocks Editor but you will not be able to connect to a device until you fix the setup.
You did not enter a location for the App Inventor Setup command directory, and App Inventor was unable to find the directory on its own.
El problema es que no se ha instalado appsetup :
aquí para descargar
Y listo… Menos mal jajajaj ya se conecta.