Actually, I've gotten same problem twice in past 12 hours. eLicenser application on the same machine shows the dongle and the licenses on it, but VE7 insists there's either no dongle or no license or that there's an USB problem. Rebooting didn't help. USB ports on that machine work well with, say, iLok and other USB thingies.
What's really peculiar is that the dongle in question works fine in other machines, and the license can be removed like nothing, transferred out and back. Maintenance is done, so it shouldn't be that.
Maybe you've tightened the screw a little too much?