Release not found

[Sascha Manns]

Hello list,

sometimes if i'm adding a new repository and make a apt update, i'm
getting errors like:

Fehl:20 http://ppa.launchpad.net/utappia/stable/ubuntu zesty
Release          
  404  Not Found
Paketlisten werden gelesen... Fertig
N: Skipping acquire of configured file 'main/binary-i386/Packages' as
repository 'file:/var/cache/apt-build/repository apt-build InRelease'
doesn't support architecture 'i386'
E: The repository 'http://ppa.launchpad.net/utappia/stable/ubuntu zesty
Release' does not have a Release file.	

But why that happens?

Greetings
Sascha