If you can link the null modem between the computer and box directly
that is your best bet.
also Jodav is right, you are using old firmware
I will send you some instructions on USB convertor cable
settings when I get home from work but not sure if you need them.
(about 4.30pm)
Have you set the baud rate (bits per second) to 115200
for the com port you are using for the USB lead.
And that also matches the com port selected
in the loader program ?
I was wondering though, if you have managed to flash
old firmware, why you can't flash the newer version.
Give the USB converter a bit of a wiggle where it meets the
null modem cable as they don't give very good connections.
make sure the box is switched off at the back, hit
download in the loader then switch box back on from the back
You said you also had a box,you can also do a "box to box" flash.
there is a thread in this section somewhere telling you how to do it.