Airtel — sim activation and network issue.

I have upgraded my sim to 4g network after that i place the sim to iphone5 then the only message pop up the screen with no sim card, to check the sim i place the sim to another mobile the sim is working properly, else i check the iphone with another sim that sim also working properly.
So what is the issue with the sim card not working in iphone solve the problem fast because its my buisness sim card.