Short description of error
I was trying to control a driver by a property of a node within a node setup. Apparently Blender rejects the data path of node properties but I couldn't found anything about such a limitation in the documentation so I suspect something went wrong here.
Other properties do work. For instance I can access all world properties except those stored in the node tree, it's the same for node based materials. I noticed the absolute data path for nodes is different from what is possibly expected by the set ID-type. Following examples are both properties of "World" from a users perspective:
But the latter one wouldn't work, neither as absolute path nor as relative one (when using "copy data path").
Exact steps for others to reproduce the error
The attached .blend file has two mapping nodes in the world shader, one of them has a driver added that should be controlled by the exact same property of the other mapping node but its data path is rejected.