Comment 22 for bug 984510

I also had this problem using Win7 64 bit. I was using a card reader that has a Micro SD slot on one end and a USB male on the other end with no other ports. I was plugging it into a USB 4 port hub when Win32DiskImager was unable to find the drive letter of the card reader. However when I plugged the card reader into a usb cable that connects directly to the PC usb port, the drive letter was recognized immediately.

That fixed my issue.