I have the same error, but I was able to solve it by editing sourceslist.py and removing the .sources disablement.
PS: I reported the same bug a bit later, but when I changed its status, the bug report disappeared. ** Attachment added: "sourceslist.py" https://bugs.launchpad.net/ubuntu/+source/software-properties/+bug/2053228/+attachment/5757429/+files/sourceslist.py -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2053228 Title: software-properties-gtk does not start To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/software-properties/+bug/2053228/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs