Ios 7 compitible app crashes on launch. Why?

I have just launched app,with IOS deplyment Target to ios 6 and latest IOS SDK 8.1. Now App runs fine on ios 8 but i have some users with ios 7, saying app crashes on launch. I have checked all code ,nothing used which was deprecated. please guide me here.

I checked back in 2013 when IOS 7 launched, Many Apps was crashing, is this problem still persist?? How do i check on device with IOS 7, I did downgrade my phone's beta to IOS 7 but my app was working fine in my phone. Cant figure problem. Please some one help me.