Thats not it, HP says its a usb2 device. I'm thinking theres something wrong with your usb2 port power, driver, or hub.
Try the device plugged into a usb2 port on the back of your pc.
I have tried in many other pc's and laptops. Its giving the same prob. working in 3.0 but not in 2.0.
Is there any fault in usb's log list or hdisk, or any other stuff like driver built in usb, etc?