Yeah, I know: I have strange hardware. Work with me, wouldja please?
I have this little card reader bolted into the front panel of the desktop. It has no trouble reading SD cards at bootup. But once the system is running, you can shove as many cards into it as you can find slots for, and it won’t read a one of them.
I haven’t figured out whether this is a hardware issue or a Windows 7 issue; chatter on the interwebs seems to blame both equally.