The firmware is for a different hardware revision (e.g., you tried to flash a DG8245W2-48 firmware on a DG8245W2-10). Fix: Double-check the sticker on the ONT. Only use firmware marked exactly for your hardware.
: VDSL2 (with vectoring), ADSL2+, and dual-band Wi-Fi (802.11ac). Hardware Interface Dg8245w2 Firmware