user deletion problem

[PM]

> That user is no longer listed in /etc/passwd?
>

Here is the complete history and error details:

myfamily at myfamily-desktop:~$ userdel -f linuxworld
userdel: cannot lock /etc/passwd; try again later.
myfamily at myfamily-desktop:~$ sudo userdel -f linuxworld
[sudo] password for myfamily:
userdel: cannot lock /etc/gshadow; try again later.

The error I am getting is this one. And the user to be deleted is
'linuxworld'
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