The appliance is still too hot. Wait and let the appliance cool down for a few minutes.
If you want to prepare hot frothed milk or hot milk again straight away, the milk jug needs to cool down for a few minutes before you can use it again. As long as the milk jug is still hot, the temperature limiter makes sure that the appliance cannot be operated. You can rinse the jug with cold water to speed up the cooling down process.