One thing you should avoid (well two things actually) are using letters A and B to assign a drive letter to your external drives and cards as Windows thinks of these two letters as floppy drives (remember those?) and will disable some functionality.

For instance, if you label a compact flash card in its readers as drive A, the Microsoft Scanner and Camera Wizard may not work and may tell you that “Windows cannot operate on this device because some of its files and folders may be secured by Windows.” It then suggests that, “To work with pictures on this device, click Start, click My Computer, and then double-click the device.”

Well, don’t resort to that, instead, reassign the device to a drive letter other an A or B (using the diskmgmt.msc command), unplug the USB cable then plug it back in, and everything should be fine.