It sounds like the twrp nandroid was corrupted. Fyi, it's a zip file so if you rename the tar to zip twrp should recognize it. Twrp and cwm nandroids are not compatible so a nandroid made in one will not work in the other.
At this point I would make a nandroid of your current rom in twrp and restore it just to confirm you have twrp working correctly. Then I'm afraid you're going to have to recreate your stock from scratch.
Sent from my Nexus 5