i'm getting this error to a few times.
i hope i can help others but i think i found the probleme.
i connected pin 2 till 13 on special relais to switch 230v.
when i disconnected all the pins everything works fine !!!!
i connected pin for pin on the board.
when i connected pin 13 the probleme is there again!!
when you put the voltage on the arduino board the led 13 is automatic blinkin a few times.
when i got the relais connected the relais switching a few times to.
i think this will make a connection fault on the usb connection.
so pull the wires on pin 13 off before uploading your sketch!!!
hope i helpt a lot of people with this.