After Rooting my phone, I get a black screen, followed by "[app] has stopped working" for every application, any idea what could be going on? I just rooted my Samsung Galaxy G4 I9500 today. It was working fine, I even restarted it a few times just to test everything was going nice and dandy. I also installed two apps to see if SuperUser was working properly (busybox and titaniumBackup) and both seemed to work fine.

Now, while trying to make a nandroid backup I entered recovery mode and touched "reboot device now". Afterwords, the device stopped starting properly.

As described in the title, the screen remains black with messages popping up saying something like "[x] app has stopped working". Trying to turn off the device gives me the usual windows (turn off/airplane mode/restart). Also, I can change the volume. Any idea of what could be going on?
I had the same problem when I flashed cmw12.1. 
I backed up that Rom and when I rebooted I got same message as you.. Everything saying "stopped working!". 
Later I noticed that my nadroid backup was on internal storage and I was running out of space. 
I deleted that backup and everything went fine. 
Move that backup file to external sd card and try rebooting again.. 
Hope that would fix it :)