Guild Wars 2

Verified. Tried 3 separate times to join Sanctum Sprint, each with the same message: ‘Waiting For Players’ at which point there were 6 other people than myself within the starting area. Waited 5 minutes minimum each time for the race to start, gave up and tried again, after waiting 5 minutes.

The event, to kill Taidha (in regards to protecting Bill & Hekja) must be completed 3 times, before Taidha can be started. According to the wiki it takes place every 5 to 10 minutes (although I have seen it take upwards of 20 at times and only after more than a dozen people came and went, trying to trigger it. As to date I myself have found no missions or bosses that can do so, you must merely wait.) Here is the webpage showing the entire list of events & more, hope this helps:
http://wiki.guildwars2.com/wiki/The_Campaign_Against_Taidha_Covington

That would be a great thing to know, as I have over 500, myself and am loathe to delete them, just in case. =/