There is no link and no menu entry for Kohacon 2012. There has been one at some point, it probably just got lost when changing the navigation.
https://koha-community.org/kohacon/ Edinburgh is listed here, but no link, presumably because the website for it doesn't exist anymore.
https://koha-community.org/kohacon12/ at least leads to this: https://koha-community.org/kohacon12-attendees/ There was more on k-c.org at some point, with the schedule, their fancy logo and all. I think they actually did not have a separate website but only used the official one. Why did it get deleted? That's strange.
See also https://web.archive.org/web/20160121052908/https://koha-community.org/kohacon/kohacon12/ and the programme here https://web.archive.org/web/20160121025923/https://koha-community.org/kohacon/kohacon12/program/
Hi Mirko, It doesn't seem to exist now. I'm quite sure I didn't delete it myself. Possibly the person who was maintaining the page deleted it. That really isn't too strange, the people writing that page would have had delete privileges. I've added a link to the internet archive page of the programme.