To know if there is a problem with the FTP connection you have to open the ms-dos prompt and send this command:
telnet myname.altervista.org 21
If the connection is successfully executed you should see a response from the server like this one:
220--- AlterVista FTP based on ....
If it does not appear there's a problem with the connection and you have to check that your network and firewall configurations allow the FTP connection.
If you have to report a problem with the connection, please add the result of this test.
Remember that FTP access is only allowed if you have an AlterSite.