Martin - I just remembered something. Unlike BeagleBone, BeagleBone Black does not come with any on-board JTAG emulation. If you want it, you need to add a JTAG header yourself.
http://elinux.org/Beagleboard:BeagleBoneBlack#Optional_JTAG
If you are simply plugging in the USB cable, trying to get JTAG connectivity, then it explains why no emulator is detected.
ki