No links could be created during the Register Raster process.
It is possible that the input raster is not a close enough match to the reference raster. As well, if the input raster is quite different than the reference raster, then it may not be possible to use that particular reference.
Make sure that the correct reference raster is being used, and that it is geographically in a similar area as the input raster. You may need to adjust the input raster (using a link table) to get the input into a similar geographic area.