Error: Cannot Communicate With Device

I have a new Kobo Touch. I was able to add about 1000 books to it without any problem yesterday. Now today, when the device is connecting to Calibre, Calibre notices it okay, but on the job Getting a List of Books From Device, it runs for a while, then gives the error -- Error: Cannot Communicate With Device.

I have rebooted the Kobo and the computer, the Kobo and its sd card are mounted correctly in Windows. What can I do to get back to normal? I have used Calibre a lot with my Kindles and my iRiver, and this is the first problem I've had with it.

Thanks!