If I remember correctly I found the code and model here: Sky Sphere Script
The right model is available to download on the last reply on that link. The code there creates a bam file with the sky-sphere however that seemed to be the source of problem. To fix it I recommend only using this part of the code:
self.sphere = loader.loadModel("InvertedSphere.egg")
# Load a sphere with a radius of 1 unit and the faces directed inward.
self.sphere.setTexGen(TextureStage.getDefault(), TexGenAttrib.MWorldPosition)
self.sphere.setTexProjector(TextureStage.getDefault(), render, self.sphere)
self.sphere.setTexPos(TextureStage.getDefault(), 0, 0, 0)
self.sphere.setTexScale(TextureStage.getDefault(), .5)
# Create some 3D texture coordinates on the sphere. For more info on this, check the Panda3D manual.
I still don’t fully understand the nature of the problem so this may not work but I hope it does.