i9505 Sim Card Removed continuosly showing

So, I have a Samsung S4 i9505 and something is bothering me too much. It continuosly shows "SIM Card removed" and I must click "Restart". I tried flashing different firmwares, from 5.1 Lollipop to 4.4 KitKat. I tried changing Sim Card Slot. It is really annoying as sometimes it shows every 5 minutes. Can someone help me?