I have this message every now and then. And ussually when it happens, the phone does not connect correctly to the computer (In windows you get the message that the device was not properly installed).
I just unplug, and plug again, and it ussually works...

The USB in my phone feels pretty tight, and the cable is new. I think is more related on how you plug the cable (fast, slow, to the side, etc). sometimes the conection is not good.