Steps to reproduce:
1) Start Netinstaller TC2
2) Choose MATE or some other DE besides gnome.
3) Begin installation process.
4) Anaconda gets the following error on "Starting installation process":
"the following error occured while installing. This is a fatal error and nstallation will be aborted. error populating transaction: failure: Packages/d/device-mapper-1.02.78-2.fc20.x86_64.rpm from fedora: [Errno 256] No more mirrors to try."
I was unable to reproduce this with an install of XFCE to a VM using the TC2 x86_64 netinstall iso.
I've also seen this in gnome installs and suspect it's a mirror issue. If you get this again, can you inspect the logs to see which mirror is being used?
Discussed at 2013-09-04 blocker review meeting [1]. This appears to be a mirror issue and does not violate any F20 alpha release criteria, thus rejected as a release blocking bug for f20 alpha.
Dan, before you propose a bug as a blocker, please make sure it contains all necessary information, like logs. It's pointless to discuss a bug that can be caused by a million of different glitches, without having some real data.
[1] http://meetbot.fedoraproject.org/fedora-blocker-review/2013-09-04/