I created ssl certification using openssl. When I try to download folder from that FTP server using Filezilla it is showing the following error log. But the files inside the folder are getting downloaded to my system. The error is

Error: GnuTLS error -15 in gnutls_record_recv: An unexpected TLS packet was received.
Error: Could not read from socket: ECONNABORTED – Connection aborted
Error: Disconnected from server
Error: File transfer failed

what is cause of this error and how to rectify it?