If you get a Root Element is missing error while starting Epicor, it is caused by a corrupted file on your local machine.  

To fix the issue:

1. Close the Epicor eror dialog
2. Browse to the path to see this file:
   1. C:\Users\<UserName>\AppData\Local\Epicor\Epicor.exe_StrongName_<RandomNumber>\3.2.700.0\user.config
3. If that file is 0b in size, it is corrupted
4. Delete the 0b file.
5. Try to start Epicor again.