If I’m understanding the issue correctly.
The active image node you have selected, the one containing the empty image you’re baking to, shouldn’t be connected to anything.
It means you’re trying to modify something that is also being read. In your case that would be because the texture you’re baking to is also being read as part of a material calculation so you need to disconnect it.
All that said, your bake results will be unusable regardless. To transfer the texture data through a bake, you first need to better match the shape of the source mesh to that of the target so that the key features align. Easiest way would likely be through the use of a mesh deform modifier followed by a shrink wrap modifier.