It works perfect for me.
My map was rotated 359º to see "right" a little section of map, but it didn't allow me to georeferencing images.
I went to Data Frame Properties -> General: and I change "rotations" 359 for 0 and tool began to be enabled.
Nice!
I've found a workaround. In the Data Frame Properties for the data frame that you need to georeference, go to Coordinate System. Expand layers, then the coordinate system assigned to your imagery, then click on the imagery layer that you want to georeference. It should change the Georeferencing toolbar from grayed out to active.