W: Problem unlinking the file lists - Clean (21: Is a directory) Error when running 'sudo apt-get update' [duplicate]

I started seeing this error msg W: Problem unlinking the file lists - Clean (21: Is a directory)

whenever I tried to update using apt.

I have already tried sudo apt-get autoremove && sudo apt-get clean && sudo apt-get autoclean

but still the problem persists.

Need help pls. I'm running Ubuntu 16.04.1 64-bit

`You can delete all files in /var/lib/apt/lists/ and re-run apt-get update.

https://askubuntu.com/questions/816503/w-problem-unlinking-the-file-lists-clean-21-is-a-directory-error-when-runn`