"Android.System.UI has stopped working" is a common error message that occurs when the update was either corrupted or unsuccessfully patched on your device. The reason this error message is shown is because Google Search(Google Now) application is not compatible with the updated UI interface that the device is running. Android is heavily built around this application, therefore it may cause headaches when this application stops working. Anyone experiencing this issue that has access to the Google Play Store, please update to the latest Google Search Application.
1) I updated, but the issues still persists...
A) If this still occurs after the application update, you will have to wait until the your manufacturer updates the Google Search application in the /System directory. You can get access to the /system directory and patch the .apk, .so, .odex files by rooting, but please do it at your own risk.
2) What is /System directory(partition)?
A) This partition contains all your drivers, kernels, system files, preloaded application, and modem. This is basically the System32 folder that exists on Windows PCs, but for Android Systems.
3) I can't access the Google Play Store because this error message pops up right after the device boots up or before the homescreen, any suggestions?
A) You will have to wait until the your manufacturer updates the Google Search application in the /System directory. You can get access to the /system directory and patch the .apk, .so, .odex files by rooting, but please do it at your own risk.
4) Who's fault is this? Manufacturer or Carrier?
A) Both. Manufacturer because they did not include updated versions of preloaded applications(GMS), such as Google Search. Carrier because they are the ones to request an update through the carrier, so if they did not specify to update these core apps, it's mostly their fault.