Texture painting from one UV map to another (to remove repeating textures)--problems

Hi everyone,

I’m trying to follow a tutorial from an older blender version that involves modeling and texturing a wooden barrel.

The point I’m stuck at involves using the clone tool (texture painting) from one UV map to another. Both UV maps use the same wood plank texture, but the idea is to paint over the repeating parts of the texture on one UV map by using a different UV map that covers different areas of the wood plank texture. This is apparently achieved with the clone brush tool, but nothing happens when I paint with the clone brush (it should be painting from one UV map to another, as I understand it).

Here is my blend file (with external data): http://www.mediafire.com/?1vvts3aq5he2kam
Here is the tutorial (the relevant part is 30:00 - 31:10): http://cgcookie.com/blender/2009/06/22/creating-a-wooden-barrel/

Here is a screenshot that attempts to explain the issue with a quick visual:

Thank you