I just came from an AT&T thread and there are bunch of people including me having it. I don't think any one knows what is causing it but if you pull down the screen you will see a message saying that an app has been forced stopped etc..... The only thing I am inclined to believe is that it is a third party application acting up. Now the error is given by Knox security and some one there suggested the following: bring down the screen... tap and press the message, supposedly a long press, that will take you Knox I believe or to the application that is causing it (don't remember which one), once there clean the cache and delete the data and supposedly that will take care of it. I haven try it yet cause it hasn't happened again.. You might want to give it a try. By the way some people said it was the wifi but let me tell you that the two times that happened to me, I was not on wifi... so I don't think that is the problem.