towelroot doesn't work on the ota update. you probably have to go back to v3 and then flash the zv4 rom to get root. towelroot worked for me after flashing the zv4 rom, but looks like from recent posts on the rom thread that the zv4 rom doesn't update the kernel. If I understand correctly, the v3 kernel can be rooted by towelroot, but not the v4 kernel.