It's possible that your cIOS didn't install correctly. Run the cIOS38rev14 installer again and see if it clears anything up. It's designed to overwrite the previous installation, so running it again is fine. Don't forget to have ios38-64-3610.wad in the root of your SD card (should still be there from the 4.2 guide, unless you removed it).
If that doesn't clear it up, it could either be that the SD card wasn't formatted correctly, or there are some minor issues with the usb drive. Have a look at the USB Devices Compatibility List to see if there are special notes about your drive, and go from there. Cheers.