"The operating system on your device is modified in an unauthorised way" System Update error on android device.

Note:
This option wouldn't work to rooted device, but it can be solved if you unroot the phone.

Steps:
1. Power off the device and access recovery mode
2. Use "Wipe cache partition "
You can also use " Wipe Data/ factory reset" , if this method doesn't work. find the procedure in the 2:26
3.use "Reboot system Now" for normal start up.
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