Hmmm, I see to have killed my 2011UiAS-2HnD by upgrading it to v6.39.2

It upgraded ok but then sat at 100% CPU for ages, then I could get at the GUI and noticed there's seemingly no Internet access. On further investigation there's an issue with the DNS settings (/ip dns).

My original DNS servers are missing from the config and I'm unable to re-add them, I just get an error. Also doing this seems to max out the CPU. If I run an /export it hangs at the "/ip dns" section.

So I want to downgrade but can't workout how to, i.e. without any Internet access from the RouterOS box.

I've downloaded an earlier version of the firmware to my PC/Mac but can't work out the easy way to actually get it onto my Mikrotik box to make it downgrade (I tried dragging it to the root of the file structure and rebooting, but this doesn't work).

Any thoughts appreciated.

Upload the package(s) and then execute: /system package downgrade
(Or equivalent in Winbox: System > Packages > Downgrade)

Thanks for the advice.

In relation to the "upload the package(s)" is that a case of placing the ".npk" in the root (which I have tried).

You should netinstall it and start clean. Most probably, NAND corruption.