While not strictly an error this status message indicates you are trying to connect to a FTP server which does not support TLS. In this case you have to change the connection encryption configuration to Only use plain FTP (insecure). However with this option all the data, including the credentials, is transferred in clear text.
Insecure server: it does not support FTP over TLS
Tags: FTP, Insecure server, insecure server it does not support ftp over tls. filezilla, this server does not support ftp over tls, TLS