My 7″ RCA tablet will only pop up “Unfortunately, UI System has stopped”. What do I do to fix it?
Unless you remember the last app used, updated, installed, or changes made to the system, it is difficult to say what may have happened. The quickest and simplest thing to do is factory/hard reset the tablet and start over.
Backup your important data and then try factory resetting your tablet.
Dealing With System Problems In Android: Safe Mode, Factory Reset & Restoring Backups