Is your erom tool the right version for that model? (they differ from model to model)
Are you using the correct firmware for that model? (afaik erom will only work with original firmware, not patched one. You'll have load patched firmware after getting original one on ariva)
Are you using a "null modem" rs232 cable. (they're a couple different rs232 cables but they all look the same)
Have you a pc with native rs232 port? (some usb to rs232 adaptors don't work, pcmcia to serial rs232 cards work)
I know that there are USB-RS232 cables that work with many receivers, but the manufacturer is the one that should at least tell us in their manuals what would be the specific reference of the cable that we would have to buy so as not to make mistakes.
Not everyone has an old PC, nowadays most have laptops that only have USB ports.