[help please] s4 lost imei but calls working

I have never seen problem like this ever.

Calls, 3g, messages... all working FINE but imei is just /01

Problem is that when i try to log on to viber, it doesnt work because imei is lost

I really dont know what is going on when i type into dialer *#06# imei is blank but phone calls and everything working just fine

Please help i dont know what to do