Upgrading Sigma Lenses Firmware

When I try to use Sigma 70-300mm lenses with 300D, I always receive Error 99.
It's common problem with older Sigma lenses.

I cannot send my lenses to Sigma because, there is no official sigma store in my country. If i send my lenses to the nearest Sigma store, it will cost me more than new lenses.

So... is it posible to upgrade firmware yourself?

They don't actually upgrade the firmware - they re-chip;replace the old chip with a new one with updated code. Newer Sigmas are coming with firmware in flash memory, I believe, but originally it was a dedicated ROM.

This is exactly as I understand it but wonder if anyone knows any factual info. about this new firmware approach, i.e. do you still send in, or do you install from your computer via USB/camera, or what?

If the firmware is on flash ROM I wouldn't imagine that you could:
A/. get it from Sigma
B/. flash the ROM yourself anyway

Why's that?

Because in the case of A?. I don't think that Sigma are going to let something like this into the hands of consumers. (Yes, I know the camera manufacturers do, but that's different). and for B/. Imagine the number of different versions there would have to be to take into account every digital model of camera, not to say the variations for each lens - the permutations are too horrible to contemplate - and the camera bodies aren't likely to have the circuitry which could re-flash a ROM in the lens anyway.
Imagine what Canon would say when you sent them your smoking 1DsMk2 with a note to the effect that re-flashing the Sigma lens didn't work properly..............​.
And before you ask how Sigma will do it, how about with a lens mount attached to a computer which reads off the information about the lens, and is then able to flash the new firmware onto the control chip - they only need lens mounts for each of the DSLRs they produce lenses for.

Took the words right out of my mouth . . .