Please make sure your SD-cards/USB-sticks are FAT32 formatted. ZENEC suggests using high quality memory product with a maximum of 32 GB capacity. Higher capacity may work also but cannot be guaranteed. Also note that the USB connection is designed for a maximum current consumption of 500 mA. This means that normal mechanical hard disks are usually not compatible because the starting current of the disk is too high. In this case, the external hard drive is not indexed.