How to fix "Unfortunately, com.android.keyguard has stopped"? Every time, after booting up my device (UbiSlate 7Cz), I receive the following error message with a black background:


  Unfortunately, com.android.keyguard has stopped.


When I tap "OK" below this message, the dialogue box quickly disappears and reappears again. I'm unable to access anything on my device. So, opening the settings app and following the steps outlined in this thread is out of my domain. 

However, I managed to open my device in recovery mode by pressing the power and volume up buttons. Even after executing the following commands in the recovery mode:


wipe data/factory reset
wipe cache partition


and rebooting the device again, there was no improvement in the situation.

Other options, I get when I press the power and volume up buttons are fastboot mode and normal boot. When I chose the fastboot mode, the device just displayed the default start-up screen. As it was showing the same stuff even after hours, I used the reset pin to turn the device off (the power button didn't have any impact during this regime). From here, I am able to do the same steps as mentioned earlier. But even after all this, the device just shows this particular error message.

While searching this site, I found this question How to fix instant lock “unfortunately com.android.systemui has stopped” on Moto G with ART which I found to be similar to that of mine but with a different error message. I find my question to be different from that because, my device didn't have ART and I'm unable to view anything unlike the OP there, who could see some apps and widgets on the home screen. Also I have a feeling that different error messages have different methods to fix.

I also had a look at these threads - How to fix &quot;Unfortunately, the process xxx has stopped&quot;?, and How to fix &quot;unfortunately , the process com.android.systemui has stopped&quot; error?, but none of the methods described in the answers resolved my issue.

It would be very helpful if you could provide any solutions to this problem.

Thank you in advance!
My solution: the error happened only when I entered a new SIM card. Without SIM cards the phone worked as expected (Alcatel Pixi 3). I had to disable sim pin using another phone, and then transfer the sim back to the mobile phone with the problem. Disabling sim pin check seemed to solve it.