Can't upgrade to MM. Getting 'Error' during process

I am unlocked and unrooted. I had previously upgraded to MM, but ran into some major problems after setting my SD card as internal, and ended up having to use the stock Lollipop tool. So, now i am running stock Lollipop and have received the OTA update. I try running it and it enters the stock recovery ok, the progress bar starts, then after a couple of minutes, i get the dead Andy icon and a quick 'Error' message. It reboots me back to Lollipop and tells me there is an update available and i can try (and fail) again if i want.

A few notes on things i tried to work around this issue (rather than solve it):
1) I have a nandroid i took while in Lollipop, I had it on my PC and i moved it to my sd card but TWRP can't see my SD Card still (E failure to mount SD card). I tried look for solutions to this, but nothing i found worked.
2) so i tried taking the stock MM ROM and moving it to my internal storage and flash that through TWRP, but I couldn't get it to appear in TWRP for selection. I tried look for solutions to this, but nothing i found worked.
3) I took my SD card out completely out, then tried taking the OTA update. Same result: "Error" then reboot.

So, any ideas on how i can get some info on what is causing the failure? Any thoughts on what i can try to resolve this?

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