Some sources are not crawled


I've just installed Autoblog (to simulate a kind of Google News for Africa) and I see that some feeds are not fetched.

Their status remain to "never", and I guess (but not sure) that it is because when they are triggered, there is still another feed source which is crawling.

So, what is the problem ? I just create 27 sources now, and I'll go to 2,000 sources at least.