Installing vsftpd - 500 OOPS: could not bind listening IPv4 socket?

I have to set up a FTP server on my machine. I have installed vsftpd using the command:

sudo apt-get install vsftpd

I then edited the configuration file vsftpd.conf in the location /etc. The file contains:

#Set the server to run in standalone mode
listen=YES

#Enable anonymous access
local_enable=NO
anonymous_enable=YES

#Disable write access
write_enable=NO

#Set root directory for anon connections
anon_root=/var/ftp

#Limit retrieval rate
anon_max_rate=2048000

#Enable logging user login and file transfers. /var/log/vsftpd.log
xferlog_enable=YES

#Set interface and port
listen_address=192.120.43.250
listen_port=21

The IP address 192.120.43.250 is the eth0 for my server. When I run the command

sudo vsftpd /etc/vsftpd.conf

I get the error:

500 OOPS: could not bind listening IPv4 socket

To check to see what was running on port 21, I ran the command:

sudo netsat -tulpn

And saw that vsftpd process id was 29383 so I issued the command:

sudo killserver 29383

And checked again. The vsftpd was still there, but with a different PID. Running the command:

sudo killall vsftpd

and

sudo killall -9 vsftpd

Does the same thing. I have already tried reinstalling. Anyone know what is going on and how to fix it?