I'd never heard of ftptest before so I decided to try it - I got the exact same error message ...
Error: Carriage return without line feed received
The replies sent by your server are violating the FTP specifications.
You have to upgrade to a proper server.
However, I KNOW my ftp server is fully functional, and externally accessible - I have kids at college in a different country who use it to get "stuff from home" when they need to, so all I'll say at this point is I'm not impressed with ftptest.
Let's look at your particular issue though - I like to test "local access" as the first step, so, uncheck the "report external ip in passive mode" box, and try to access the ftp server by it's internal ip address, make sure that works before you do anything else, and then recheck the box and test it from outside.
Based on the test results from ftptest.net, it looks like you have your dynamic DNS & port forwarding setup correctly, I see no reason why it should not work.