Trying another cable, if you can't try another USB port, is one of the first things to do when something doesn't work as expected.
Glad you solved it!
I have some spare USB A-A cables, but I had none USB A-B cables since, I can connect to printer by WiFi and this one USB A-B cable I bought month ago just for Kemper.
I just don't know this faulty cable works with printer... anyway today I noticed that after connecting Kemper with RigManager with this cable the Kemper device was present in Windows 7 Device Manager for a while, but after some time it was dropped. The device got exclamation mark and I got Windows dialog with info that "diver could not be installed", though the device was with proper driver 10 seconds before.
Dosen't matter now Check your cables guys!