If your hardware is indeed set up and plugged in properly then that error means it cant see it.
I'll admit I am not really familiar with the items you appear to be using and you didn't give much of a description of what you were doing with what devices.
With devices that have currently been working this either means a power loss on the device or a broken com cable. If the device is integrated it means that the device died. It will need replaced.
Sometimes wriggling connections or connectors will get a device working again for a while. It is usually only a matter of time before another failure though.