rotating UIimageview on a button click??

Question

i found a code snippet through which i could rotate an uiimageview on this link rotate an image

but whenever i call this method on my button, simulator gives an uncaught exception?? what could be the reason for this??

-(IBAction)clickme:(id)sender

{

[self spinlayer:img.layer duration:1 direction:SPIN_CLOCK_WISE];

}