This error appears when the FTP control connection is initialized from IP1 and the data connection is initialized from IP2 for PASSIVE FTP.
In these cases vsftpd detects that IP1 and IP2 are different so it terminates the connection.
TO disable this check, add
to vsftpd.conf and restart it.
Set to YES if you want to disable the PASV security check that ensures the data connection originates from the same IP address as the control connection. Only enable if you know what you are doing! The only legitimate use for this is in some form of secure tunnelling scheme, or perhaps to facilitate FXP support.