I have the UK unlocked variant, single sim a5_dug so it's a supported model as far as I'm aware. My bootloader is unlocked, s-on, I have a custom recovery but do not have SuperSU installed and I am currently not using any custom ROM or kernel, just the stock HTC ones (CM would be my first custom ROM).
I make a back up for my current ROM using CWM.
I then format/factory reset using CWM.
I then clear the cache partition using CWM.
I then clear the Dalvik cache again, using CWM.
And then I go to install via zip using CWM, select the latest nightly (which I downloaded from the CM website) for the Desire 816 and then as I stated, it almost instantly aborts.
I've tried this 3 times now and the same results keep happening. Luckily I backed up first obviously so I don't have a bricked phone. But I would like to give Cyanogenmod a try.
Does anyone have any advice? It'd be greatly appreciated!