According to the manual solid red LED means an internal communication error. The good news is it sounds like your set up is working, i.e. you are running the ros sweep code and usb port is opening, the bad news is I don't know if I can help you. A red light could mean a number of things.
A random thought, how are you powering the device? Supposedly it can draw up to 650mAh which means that if you are running on an old usb port it may not provide enough power. Maybe try a different usb port, a newer computer or an external power source?
Anyone else have any thoughts?