Invalid configuration for device '0' with ISO in Content Library on vSphere-ISO

I have a issue very similar to this one but are issues are different.

I am trying to use vsphere-iso with an ISO in a vSphere Content Library and when I use the apparently correct format in "iso_paths" for the ISO I get Invalid configuration for device '0'

I am successfully about to use the same ISO from a datastore, but not a Content Library.

Is this because I am using an ISO and not an OVA/OVF? Or am I doing something else wrong?