Unable to connect to FTP server using Filezilla with router in-between

While connecting to my web server using filezilla, i am getting this error:

Status: Resolving address of ftp.mysite.org.in
Status: Connecting to 199.199.199.18:21...
Status: Connection established, waiting for welcome message...
Response:   220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
Response:   220-You are user number 1 of 150 allowed.
Response:   220-Local time is now 17:58. Server port: 21.
Response:   220-This is a private system - No anonymous login
Response:   220-IPv6 connections are also welcome on this server.
Response:   220 You will be disconnected after 5 minutes of inactivity.
Command:    AUTH TLS
Response:   234 AUTH TLS OK.
Status: Initializing TLS...
Error:  GnuTLS error -9: A TLS packet with unexpected length was received.
Status: Server did not properly shut down TLS connection
Error:  Could not connect to server

I use a cradlepoint CTR35 wifi router to connect to the wired internet connection.
When i connect to the same server without this router, the connection works flawlessly.

So i guess there is some problem with my router firewall settings, but i dont know what!
Can somebody help me out please?

Note: The server requires EXPLICIT FTP OVER TLS and does not work with plain FTP sessions. And i can connect to other servers using plain FTP with the router in between.

EDIT:

Okay. here is some debug info..

Status: Resolving address of ftp.md-47.webhostbox.net
Status: Connecting to 199.79.63.83:21...
Status: Connection established, waiting for welcome message...
Trace:  CFtpControlSocket::OnReceive()
Response:   220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
Response:   220-You are user number 1 of 150 allowed.
Response:   220-Local time is now 05:11. Server port: 21.
Response:   220-This is a private system - No anonymous login
Response:   220-IPv6 connections are also welcome on this server.
Response:   220 You will be disconnected after 5 minutes of inactivity.
Trace:  CFtpControlSocket::SendNextCommand()
Command:    AUTH TLS
Trace:  CFtpControlSocket::OnReceive()
Response:   234 AUTH TLS OK.
Status: Initializing TLS...
Trace:  CTlsSocket::Handshake()
Trace:  CTlsSocket::ContinueHandshake()
Trace:  CTlsSocket::ContinueHandshake()
Trace:  CTlsSocket::ContinueHandshake()
Error:  GnuTLS error -9: A TLS packet with unexpected length was received.
Status: Server did not properly shut down TLS connection
Trace:  CTlsSocket::OnSocketEvent(): close event received
Trace:  CRealControlSocket::OnClose(10053)
Trace:  CFtpControlSocket::ResetOperation(66)
Trace:  CControlSocket::ResetOperation(66)
Error:  Could not connect to server
Status: Waiting to retry...