Ok, my problem seems to be similar to this, and this, but following the answers, there is not helping me. This might be because I am using Xcode 5, before I upgraded to this
I had the same issue, and the "Use Asset Catalog" worked for me. Maybe take it out of the resources, put it back in, clean, build and then see if it works.
To find this button : Project > General > App Icons and Launch Images