[GRASS-user] Cannot re-install Grass 7.2

[Mira Kattwinkel]

Dear list

I would like to go back from Grass 7.4 to Grass 7.2 (because the new 
version is incompatible with QGIS). However, I have severe problems.

I am running Linux Mint 18.2****(Sonja).


When I try to add the correct ppa I get the following:

mira at mira-mint ~ $ sudo add-apt-repository ppa:ubuntugis/ubuntugis-stable
Cannot add PPA: 'No JSON object could be decoded'.


Changing the source manually in 
/etc/apt/sources.list.d/ubuntugis-ubuntugis-unstable-xenial.list to

deb http://ppa.launchpad.net/ubuntugis/ubuntugis-stable/ubuntu xenial main
deb-src http://ppa.launchpad.net/ubuntugis/ubuntugis-stable/ubuntu 
xenial main

has the following effect when running sudo apt-get update:

... Err:16 http://ppa.launchpad.net/ubuntugis/ubuntugis-stable/ubuntu 
xenial/main Sources
   403  Forbidden
...

W: The repository 
'http://ppa.launchpad.net/ubuntugis/ubuntugis-stable/ubuntu xenial 
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://ppa.launchpad.net/ubuntugis/ubuntugis-stable/ubuntu/dists/xenial/main/source/Sources 
403  Forbidden
E: Some index files failed to download. They have been ignored, or old 
ones used instead.


Can anybody please point me into the right direction? Thanks a lot,

Mira