Error when activating encryption

Hey guys!

I am new to nextcloud. I tried to activate the encryption as it is shown in the Manual. but when I log in again after Setting it, I get the following error “Falscher privater Schlüssel für die Verschlüsselungs-App. Bitte aktualisieren Sie Ihren privaten Schlüssel in Ihren persönlichen Einstellungen um wieder Zugriff auf die verschlüsselten Dateien zu erhalten.” - “Wrong private Key for encryption app. Please set a new private key in your personal Settings to get Access to your encrypted files again”.

Does anyone know what to do?