When i have  connecting  sftp in filezilla for upload files into server,  it could not be connected,  after that check in secure log file  in server showing below error,

 # tail –f /var/log/secure

Apr  1 16:53:42 host proftpd[1234]: host.domain.com ([]) - USER proftpd (Login failed): Invalid shell: '/bin/false'

find the protpd.conf file, If unable to find the proftpd configure file you can find it by using below command,
# proftpd –V

Configure : /etc/local/proftpd.conf
# vi /etc/local/proftpd.conf

Suppose the /bin/false is not listed in your /etc/shells file.    For proftpd, it shouldn't even be checking this,  

RequireValidShell  no

Append following line in proftpd.conf

Restart proftpd to take effect changes we've done..
# pkill -9 proftpd  

# proftpd

Note : Check the proftpd  status  with netstat command.
# netstat -lnp | grep proftpd

tcp    0    0*       LISTEN      14538/proftpd

I hope you have never facing this connection issue.