This is the error I get:
Err:7 http://deb.playonlinux.com etch/main i386 Packages
404 Not Found [IP: 51.254.83.230 80]
Ign:8 http://deb.playonlinux.com etch/main amd64 Packages
Fetched 6,030 B in 6s (876 B/s)
Reading package lists... Done
W: The repository 'http://deb.playonlinux.com etch Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch http://deb.playonlinux.com/dists/etc...-i386/Packages 404 Not Found [IP: 51.254.83.230 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.

I've tried unistalling playonlinux (since I don't use it), and other things, but didn't work.
What can I do?
Thanks

You need to remove the repository from your software sources.

What distro (and version) of Linux are you running?

How do I do that?
Deepin OS 15.3 64bits

Ah, ok. I don't know Deepin, how it arranges its repositories, and whether it has software-sources installed. Do you have Deepin Software Center? If so, it may have a Repository button that allows you to manage your repositories.

In the meantime, can you please post the output from the following:

cat /etc/apt/sources.list

ls -la /etc/apt/sources.list.d

Cheers.

1st command:
## Generated by deepin-installer
deb [by-hash=force] http://packages.deepin.com/deepin/ unstable main contrib non-free
# deb-src http://packages.deepin.com/deepin/ unstable main contrib non-free

2nd command:
total 16
drwxr-xr-x 2 root root 4096 Feb 13 10:11 .
drwxr-xr-x 6 root root 4096 Feb 14 14:47 ..
-rw-r--r-- 1 root root 42 Oct 15 2011 playonlinux.list
-rw-r--r-- 1 root root 54 Feb 14 14:14 spotify.list

I have Deepin Store, but it does not have such button.

Ok, run:

sudo rm /etc/apt/sources.list.d/playonlinux.list

Then run

sudo apt-get update

sudo apt-get upgrade

It worked!! Thank you very much!! I've read a lot of posts dealing with this issue and tried several things and didn't work. This worked just fine! Thanks again!

Great news!

Please remember to mark the thread as "Solved" (see "Thread Tools" at the top of the thread).

You dont need -get part when installing:

sudo apt update

sudo apt upgrade