This was fixed in the relevant Python library packages just before Herd 1, but the fix didn't quite make it in for (only) amd64. Try later builds.
** Changed in: ubiquity (Ubuntu) Status: Needs Info => Fix Released -- installer fails to launch in Feisty Herd 1 on amd64 https://launchpad.net/bugs/78004 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs