GPU Geometry Clipmaps

I received a new 6200 with SM 3.0 and i just restarted working on my implementation of GPU geometry clipmaps "Terrain Rendering Using GPU-Based GeometryClipmaps". As you can see in the screenshot, i have problems during the update with the coordinates system and the average of the coarser elevation map. There is a lack of information in the paper, the shader code on the GPU gems II and the demo doesn't give explanations of how it works.

Edit : After a few tries, i almost fix it but i still get errors when uv coordinates cross the boundary of the texture.