A customer was attempting to update Windows CE 5.x on their GCM board using an SD card. But the SD card was not being "seen" by the GCM during the boot process, so the update wasn't happening as expected. However, after CE did boot, the SD card was seen by the File Explorer app.
Solution: The card being used for the update was an 8GB SDHC card, which was not compatible with the current bootloader, but was compatible with CE 5.0.xx. Using a 1GB SD card worked and the customer was able to update their GCM board.