JFTP connect: Bad response in Joomla 1.5 - 1.5.18 the following error message appears:

An error has occured
JFTP::connect: Bad response.

Most people in many forums talked about the CHMOD of a Unix Server not beeing set right.

Remember to set the server rights:

• the directories should be set to: CHMOD 755 (not 777 - which would make them to be open for all*)
• most files should be set to: CHMOD 644 (any other, higher number, is a security risk)
• You mostly can set the configuration.php file to CHMOD 400 and the site still works, but nobody - even not yourself - can change the configuration file, unless you change the rights via FTP back to 644.

If this does not help go to admin/global configuration and delete the FTP settings (only user and password) and safe this configuration. That should help.