It said the same thing when I uploaded the sample for "Battle In The Snow" and worked when I tried the day after. Let's hold on for 24 or 48h. If it's still unavailable I'll try again, and perhaps in Ape form.
... I wouldn't be surprised if such a site checks and makes a few retention about Flac files... All is falling down my boys !
Edit: No, I think I'll try in Ape right now, there's a problem with another of my sample in Flac when the wav. ones are ok (weird idea, I know).