I had the same problem and on top of that no sound when I bought a second-hand plugiator some time ago.
Running Mac OS 10.6.8. First I opened up the unit and reseated all connectors.
Hurray, sound but still no connecting to the software through USB.
When I tried MIDI it suddenly worked and the Plugiator registered beautifully.
After that, USB suddenly worked fine and has been ever since.
Strange but this did the trick for me.
Discuss the Creamware ASB and Klangbox hardware boxes