[2.01 JB+] Can't see /etc and some other folders

[siealex]

After flashing 4.2.1 I can't access /etc, /d and some other folders in / using "low level" setting. What's this?
PS. I can see all these folders with "low level" OFF.

[ghisler(Author)]

I had this problem too after applying the over the air update on my Nexus 7: The problem is that the superuser program (su) gets overwritten by one without root rights. OTA root keeper failed to fix that. I solved this by re-flashing CWM-SuperSU-v0.98.zip.