I experienced this problem whilst attempting a system update on a tablet (Presitigio Multipad4) running an old version of Android which I think is what caused the error (botched system update).
The problem was so bad on this tablet, that the error was flashing up literally every SECOND with the OK button and it was very difficult to navigate settings or do anything whilst their error was ocurring.
Using the "reset" pin hole on the tablet, rebooting etc, all had no effect.
The only thing I was able to do, and which others in this situation might find help is this...
Go into settings, go to "Backup/Reset" and select "Factory data reset" option under Personal Data. You will see a screen with one button "Erase Everythng". Clicking that will erase all the apps, updates, personal data etc, and restore the tablet back to it's original factory state (i.e. clean and working fine again).
Note: This is a drastic FINAL RESORT step (if you have personal data) so I would remove your SD card first, and hopefully you will have backups of your photos/contacts etc on Cloud or another service or your SD media.
Once the Erase Everything procedure is completed, the tablet will automatically reboot itself and you should be presented with the "Setup" Android screen (like when you first received the tablet, you need to setup language, time/date, WiFi, accounts etc).
Tip: It is VERY difficult even to perform this procedure (and get into settings) if like me, you get the error flashing up every second. I found two things which might be helpful to anyone in total despair out there:
1) When you reboot the tablet (before the Erase Everything and whilst the error is going) the error is slow to begin with (the intervals at which it re-appears) so don't waste time, go straight to settings the quickest way possible and scroll down quickly.
2) Perseverance is KEY, and being QUICK at pressing the options you need, after clicking OK to get the error message out of the way. The system won't do ANYTHING whilst the error message and OK button is there. You literally have MILISECONDS to click OK and use the tablet. Just keep at it, and you will succeed!
Hope that's helpful, finally after almost giving up, and 2 hours later, I have a functional, fast tablet, reset back to factory settings.