What is this bad archive mirror error

    I am installing via usb dual boot, installing graphical and getting this error. I am from India and am not able to proceed further, Could anyone please help, also attached the image  

I have same problem, i tryed to install  2.8.2  and 2.8.0 freshlly downloaded from websites. I used Rufus to burn it to USB flash disk (no problem), when i insert it to computer (Dell 7010) and try live version everything work great, latency test and even internet. But when i try to install it and have connected internet cable to computer, installer freeze for 10 minutes (same behavior when i tryed to install on my main computer). When i disconect internet cable it show that no network was found and proceed to next step. 

It seems that everything is installed but then i get same error as shown in picture above. When i want to proceed without this step it stop on next step "GRUB installation failed"

I noticed that everywhere is "-amd64" (on live version etc.) but i have intel CPU, did i done something wrong ??

By "official" you mean linuxcnc.org/downloads/ ?
I tryed that "LinuxCNC 2.8.2 Debian 10 Buster PREEMPT-RT ISO", but with no luck.
I tryed to install Ubuntu 20.04 LTS with no problem, same proces, download on windwos computer, burn to USB with Rufus boot and install, no problem at all. I only think that i saw some error lines when booting but they disapear so quickly that i didn't even had time to recognise what is going on.

So it's there some easy way how to instal LinuxCNC on already installed Linux (Ubuntu, but i can try to install other one) ??

I suspect you do not have internet. Perhaps a driver did not install for your network card. I saw that on the weekend. What PC and do you know what ethernet chip is used?