Perhaps this is just the case of having too many USB devices. I have lots of USB devices connected and I see my cameras (not uArm) drop connection and not being recognized.
Not all USB ports are equal. The front USB ports deliver the least power and are very unstable for power demanding devices. So only plug the mouse and keyboard and usb drives to front USB ports.
Plug uArm only to the back USB ports. If you have no more back USB ports, get a powered USB hub and plug to the back USB ports (plugging to the front USB ports does not make them better).