服务器正常，FTP无法链接，都有哪些问题导致？

Ruclinux

服务器没有问题，能正常连接，网站能够打得开，Kloxo管理后台能登录，但是FTP空间无法登录，用户名和密码正确.FTP用户状态也是开启状态。都是什么情况会出现这样的问题呢？谢谢....
[右] Connecting to root -> IP=***.***.***.** PORT=21
[右] Connected to root
[右] Connection failed (Connection closed by server)
[右] Delaying for 10 seconds before reconnect attempt #1
[右] Retry attempt Aborted
[右] Connecting to root-> IP=***.***.***.** PORT=21
[右] Connected to root
[右] Connection failed (Connection closed by server)
[右] Delaying for 10 seconds before reconnect attempt #1
[右] Connecting to root  -> IP=***.***.***.** PORT=21 (attempt # 1)
[右] Connected to root
[右] Connection failed (Connection closed by server)
[右] Delaying for 10 seconds before reconnect attempt #2
[右] Retry attempt Aborted
[右] Connecting to  -> IP=***.***.***.** PORT=21
[右] Connected to
[右] Connection failed (Connection closed by server)
[右] Delaying for 10 seconds before reconnect attempt #1
[右] Connecting to  -> IP=***.***.***.** PORT=21 (attempt # 1)
[右] Connected to
[右] Connection failed (Connection closed by server)
[右] Delaying for 10 seconds before reconnect attempt #2
[右] Retry attempt Aborted

软件风暴

21'?

Ruclinux

楼上的意思是说21端 **口被封？