I'm sorry to say there are pages and pages of people trying to get this work
there is something about Linux that won't let it work
this includes windows emulators on Linux
how ever if you can just fine a real native windows pc it should work
I have found sometimes you need incognito in Firefox "disables cache"
other have said IE mode in edge
I have used IE 9 in the passed as well
here is a decrypted firmware file if you need to go back
http://luckys.onmypc.net/openwrt/DIR-2640/DIR-2640_REVA_FIRMWARE_1.11B02.decrypt.BIN