hey fella, I can't really say exactly what the problem is, but have had rendering problems myself, which usually results in a blue screen, and my powercore driver is usually the problem. sooo..

Reload all your drivers, check driver conflicts and remove any webcam drivers (Labtec drivers mess up midi in ableton).

If that doesn't help, search the forums at www.ableton.com, there might well be the exact same problem already posted, as I saw quite a few similar problems when I searched recently.

It could be the free plugins, or one that is knocking the rest of the automation out, so turn one off at a time and render the output to isolate the problem if it is a plugin, at least you'll know where the problem lies.

Let me know how you get on.