A download manager is a program that acts as a browser plugin or addon, promising to make downloads faster, or make it possible (or more possible) to resume downloads, etc. They have nothing to do with bittorrent - a "download manager" is for normal downloads, not bittorrent. They're also sometimes called "download accelerators"
Download managers in general aren't very good at what they claim to do, and cause a lot of issues (and that's the ones that are legit). I recommend avoiding them like the plague.
So now on to why you can't access the FTP site...
Can you access any other FTP sites? (Like this one - ftp://ftp.adobe.com/ - No particular reason I picked that one)
What kind of internet connection do you use?
Are you tethering to a mobile internet connection? (using your smartphone to provide internet access to your computer)
Are you on a corporate or university network that might block FTP?
What security software are you running?