I had that happen today, quite randomly and the things mentioned in other threads didn't help. I tried different USB cables, different ports and different devices, uninstalling all, Windows Update service was running ok, etc. but I always got the same USB not recognized / device descriptor failed error in Windows 8.1 64-bit, even though I hadn't changed anything related to the Kemper for quite a while. Just randomly did that now.
What did help in my case was to:
1. Unplug the USB
2. Upgrade the Profile OS from 7.5.x to the latest (8.0.5) using a USB stick on the back of the profiler
3. Uninstalled everything related to Rig Manager (not sure if necessary, but that's what I also did)
4. Reinstalled the latest Rig Manager (3.0.145)
5. Plugged the USB cable again (first Profiler, then PC)
6. Now it was detected successfully by Windows
Maybe it helps someone