Vector Blur node makes all go blank

Sup? I checked the Testing Builds forum at blender.org/forum today and found the OSX gcc4.0 builds of Blender with the nodes and renderer etc, so I’ve been messing with it today. I’ve been using the nodes for a good few hours now, and I can get the rest to work, but whenever I hook up a vector blur node, it makes the Composite the Viewer and the Render go completely blank. Can anyone help?

you need to make sure that you render the vector output, go to the render layers tab in the render buttons, then turn on the “vec” button next to “combined” and “z”

Thank you!! That’s got it solved!