Comment 3 for bug 2062042

Thanks. I was able to re-produce this using your sources. The problem is that you have a mix of .sources and .list PPAs enabled, and since there are at least _some_ .list still present, the upgrader expects Ubuntu sources to be present in a .list file (even though they are already found in /etc/apt/sources.list.d/ubuntu.sources).

So, this is clearly a bug in ubuntu-release-upgrader. But, as a workaround, you should be able to either (a) temporarily remove your /etc/apt/sources.list.d/*.list files, or (b) convert them to .sources. The upgrade should work after that.