Updating OTA after changing /etc/system files I manually modified /system/etc/mixer_paths.xml in order to boost volume on my Nexus 5 when listening to music with a headset. As a result I am still running version 4.4.2 as whenever I attempt to update OTA I get "Error!" screen. I suspect it has something to do with my modification of the system files but am not sure. So I have two questions:


What is causing the update to fail?
How can I fix it?


I would like to do both of the above without loosing any of my data/applications.

(I would not be surprised if a question similar to this one has been asked before Android SE, but I lack experience to determine which of the questions that already exist is actually the same as my question.)
As far as I know, you first need to unlock bootloader to root a nexus device (I'm not a nexus user). 

Now, in order to update your OTA, it is mandatory to lock the bootloader and then perform the update. 
I'm a HTC user, and I faced the same issue. What I did was flashed the stock recovery, locked the bootloader and performed the update. Everything went smooth. 

I'm sure nexus follows the same path.