I am in the same situation, but can't figure it out.... I wanted to upgrade to Kitkat so I downloaded Supernexus 4.0 but the install from zip fails everytime I attempt it.. So I'm stuck in the CWM and I don't have a backup ROM to install...
I checked the md5 sum of the ROM, it's ok.
I wipe the /data partition, the cache and the dalvik cache before installing from zip..
I installed the last CWM version (v18.104.22.168).
I don't know what to do next because the only ROM I have in my phone is the supernexus 4.0 which cannot be installed and I cannot mount my phone using "mount USB storage" in CWM, my PC doesn't see the phone mass storage..
Any idea ?