The error you are getting from SNP is due to the seismic collection of the cube not being the same as that used by the horizon. If your seismic cube is contained within a sub-folder, then this error will occur. I can reproduce it with the following setup:
The ‘Coloured-AI’ cube belongs to survey ‘Survey subfolder 1’ rather than ‘F3 Demo’. When SNP runs, it checks to see whether the Horizon and input cube reference the exact same seismic collection. A workaround is to place the volume you want to work with in the same seismic collection as that used by the horizon as shown below:
