Good news - bad timing

Today I talked to one of my professors about a work experience opportunity. I don't know how much I should write about it yet, but the job includes helping out in hosting a big ethnological event here in Turku in June. It seemed very exciting, so after the talk I was very happy to learn it seems I'm being recommended for this. There are only two downsides to it: 1. The work is unpaid. This I as OK with, as I still see it as a good experience, and the deal also includes free participation (when possible) in an event that would otherwise have you pay an expensive fee. But then I noticed downside 2: The symposium coincides exactly with the Sensei course in June... This is one of the biggest karate happenings of the year, and since i started practicing I have missed it only once. Both happenings are major events in their respective area, that I should partake in. So frustrated now!