Do this test: Bug Report instructions & sample image Is the result True/False?

If false then see the UPnP section of this post: Connection problems? Check here first! (click on link)

You may need to reduce upload & downld bandwidth slightly. Also, it might be worth disbling ultrapeer abilities under the Speed options of your LW preferences.

I would also recommend not using the Resume/Find Sources function on all your incompletes simultaneously or this will definitely hog your bandwidth & use up a lot of LW's & your computer's resources.