I had that kind of problem lots of time. 90% times it was distraction errors :)
There are lots of possible reasons. Here's are the ones I've seen :
- You forgot to include the image to bundle
- Your image is corrupted
- You are using photoshop and you saved your image to PSD with a png extension (mac OS show preview of PSD files).
- You forgot to add your view to a superview (arrives sooo often)
- Wrong file name (imageName.png instead of imagename.png)
- (from Ankit Srivastava) no memory allocated to imageview
- ... if I remember some other i'd edit the post.
Hope this helps