OKay, I had this same problem with my Pfaff and what I did was this - I put the cable into a different USB port - I turned the machine off and on - I straightened the cable from the machine to the computer many many times and it finally worked correctly.
I don't know why these are so sensitive...I really don't but keep trying...and when you find the USB port that works do not and I repeat do not forget which one it is or you will have to start all over. I leave my cable attached to the computer now.
Once in a while I still have to straighten the cable where it attaches to the sewing machine but mostly it works okay now.
If you can't get it to work, take it back to your dealer - machine and all and have them help you. My dealer when I talked to them over the phone didn't have any idea what I was talking about and as I am very stubborn I just kept trying and trying till it worked.