Also I have had this problem in the past.... what do you have for network connections? Do you have more then one network setup on that computer? Do you have it plugged in where there is a router that is not liking the IP range? I have found that I have to turn off all other networks on the Host computer to get the device to upload the firmware.... Please try a few things and als know that it takes time to make things better and we are here to help you (I feel your pain)
I posted the details to this earlier. I have full communication with the g100 outside of mach3. I can ping it, I can bring up the download web page. I have quadruple checked that the firmware is correct, and can confirm that the size listed in the download manager matches the byte size in the zip file, and matches the screen-shot in the manual.
There is no network, router or switch anywhere. The computer is off the LAN and is plugged directly into the G100 with a cross-over cable. There are no other network interfaces on the computer.
As I said previously, it does eventually sync up if I leave it for a few hours, and once it's sync'ed, I can drive the machine with no apparent problems. This seems to me to rule out network problems.
The network sniff trace I posted earlier seems to show fairly clearly to me that the mach3 plugin simply has the timeout's wrong: It's just not waiting long enough for the G100 replies.