It sounds as though the connections from those two computers were multiple connections. This can happen if running more than one instance of FTP on each computer. It can also happen if your FTP client opens multiple connections (threads) in order to increase your throughput (and many do this!).
The immediate solution is to log into the shell and identify, and kill, those processes. If you cannot do this, you will need to contact support and ask them to do it for you.
To prevent this in the future, just keep your concurrent user connections to less than the limit (by not running multiple FTP clients and/or limiting the number of connections your FTP clients are allowed to use in the FTP client program's settings).
--DreamHost Tech Support