VSFTPD cap_set_proc and dead but subsys locked errors and solution

VSFTPD is the one of the easiest and secure FTP server out there. However today it bumps back with two errors.

#1: 500 OOPS: cap_set_proc error

After successful user login vsftpd will display an error:
$ ftp ftpserver.xyz.com
Output:

Connected to ftpserver.xyz.com.
220 (vsFTPd 2.0.5)
Name (localhost:vivek): vivek
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls
500 OOPS: cap_set_proc
ftp: bind: Address already in use

cap_set_proc is POSIX capability manipulation on processes function (related to filesystems but I am not sure). After searching bit I found the solution. You need to load the standard Linux capabilities security module:
# modprobe capability

#2: vsftpd dead but subsys locked error

This is another error - one of my clients was receiving while starting vsftpd. There was already ftp server running and address 21 was bind to this ftp server. So vsftpd dead but subsys locked error was generated. xinetd was configured to run wu-ftpd (quite old ftp software). Solution was simple I had removed the wu-ftpd.