setShadowOffset crash on iOS 3.x

Terminating app due to uncaught exception 'NS开发者_运维知识库InvalidArgumentException', reason: '* -[CALayer setShadowOffset:]: unrecognized selector sent to instance 0x2f86d0'

cell.shadowView.layer.masksToBounds = NO;
cell.shadowView.layer.cornerRadius = 10.0;
cell.shadowView.layer.shadowOffset = CGSizeMake(0, 2);
cell.shadowView.layer.shadowRadius = 6;
cell.shadowView.layer.shadowOpacity = 0.5;

Read CALayer class reference everything is written in the apple's documentation.