Description
The spatial reference of the Input Space Time Cube is incompatible with the spatial reference of the output coordinate system and cannot be reprojected. To complete the analysis, the calculations have been carried out in the WGS_1981_Web_Mercator_Auxiliary_Sphere coordinate system.
Solution
If you want to use a coordinate system other than WGS_1984_Web_Mercator_Auxiliary_Sphere, consider reprojecting both datasets into an alternative coordinate system to which both inputs can successfully reproject.