Unown source button grey

[AC Question]

Lost Google play store, Facebook, and loads of apps on my galaxy Tab 4 managed to get some back on but unown button in settings is greyed out won't let me select it any ideas for a fix

 

[B. Diddy]

Welcome to Android Central! Go to Settings>Security>Clear Credentials, and see if that helps.

Can you also give more details about what led up to the tablet losing the Play Store and those other apps? What did you have to do to get them back?