All datasets in the mobile scene package must use the same coordinate system. This includes both the horizontal (x,y) and vertical (z) coordinate system. Nonpackage data can be reprojected by the tool, but scene layer packages and tile packages cannot be reprojected.
Change the scene's coordinate system to that of the tile package or scene layer package. See Specify a coordinate system for detailed steps. If the scene and package horizontal (x,y) coordinate systems match, confirm that the vertical (z) coordinate system matches as well.
Alternatively, re-create the tile package or scene layer package in the desired coordinate system.
See Create an offline scene for information regarding creating tile packages.
See Create a scene layer for information regarding creating scene layer packages.