just in general - this error happens if any of the sources you specify as Instancing Ops have a different amount of data points in them. In Bileam’s tutorial you are using TOPs for the instancing so most likely some of the TOPs you are using have a different resolution. You can always check by middle-mouse-clicking onto the operator and checking the resolution and the pixelcount there.
For Instancing to work, all operators uused as a source must have the same size.