I see Niklas and Sai are already helping you out but just in case ...
Which version of Apache Ftpserver are you using? We had some issues
with passive data transfers ( related to SSL connections). Are you
using plain or SSL connections?
As Niklas said, netstat -an report would be of much help.
I'm unable to create a dump thread currently.
I did managed to reproduce it locally, and I've attached the code.
Please see it and let me know if you find any issues.
In the sample code I'm using the dbUserManager (as on my server), and trying to
login 100 simultaneous connections.
Another
