I'm getting this too, but only since I upgraded to the latest version 4.6.0 for OSX a few days ago. I hardly ever had this but now I can't wander off and leave things to download, I have to sit here hitting "Try to reattempt a Download" on every download every 30 - 60 seconds or so. It manages to reconnect every time so there's obviously no REAL busy hosts involved.

Really annoying.