The input raster is missing the vertical coordinate system.
The vertical coordinate system of the input raster is used internally to compute the Z factor and the height of the target locations. Assign a vertical coordinate system for the input raster if it does not have one.
To add a vertical coordinate system, use the Define Projection geoprocessing tool. In the first parameter of the tool, specify the raster dataset as the input dataset. In the second parameter, click the Properties button. The Spatial Reference Properties dialog box opens. Click the Z Coordinate System tab on the dialog box and choose the Z coordinate system.
If the vertical coordinate system of the input raster is left undefined, the tool will still execute, but it will assume that the Z unit of the input raster is the same as its XY unit.