mobile

Hey, hope someone here can help me out.
So I got TWRP working, I wiped my phone (and didn't make a backup, believe me I feel incredibly stupid for this) and now I'm trying to get a custom ROM to run on it. Problem is I keep getting these errors when I try installing them.

detected filesystem ext4 for /dev/block/platform/msm_sdoc.1/by-name/
unmount of /system: Invalid argument
unmount of /system failed: no such volume
E:Error executing updater binary in zip '/external_sd/cm-12-20-150417-NIGHTLY-trltetmo (1).zip'
Error flashing zip 'external_sd/cm-12-20150417-NIGHTLY-trltetmo (1).zip'
Updating partition details
E: Unable to mount '/system'

I've been looking for a solution for a few hours now and can't find anything. Any help would be super awesome.

Thanks