Cant connect to proftpd server
 

I have set up a proftpd server in my linux
I can always access it by that computer through firefox

but if I go outside and use other computer I cant connect to it.

When I connect from outside I have to wait for a long time and then it said connection reset and receive error response. However, sometimes it does work!

can anyone help me ?

Sometimes I can access it outside but sometimes error occurs. However, if I access it by that server computer using gFTP, it always works

the Error message appears when I use WS_FTP to access is as followings

Finding Host peter5.no-ip.com ...
Connecting to 61.10.153.32:21
Connected to 61.10.153.32:21 in 0.000000 seconds, Waiting for Server Response
220 ProFTPD 1.2.8 Server (ProFTPD Default Installation) [cm61-10-153-32.hkcable.com.hk]
Host type (1): Automatic Detect
USER httpp
Error reading response from server.