I\'m probably missing something obvious here, yet I\'ve been unable to solve the following problem:
I have a project with image resources for both normal and retina
Multipage TIFFs are only for OSX; they don't work on iOS.
So you need to stop trying to access resources that are, by their very nature, inaccessible, and do things the right way!
You need to open the project that generates the external resources bundle, select the target, go to Build Settings and then the Deployment sub-heading, and set "Combine High Resolution Artwork" to No. Then recompile the external resources bundle.
In your main project you should now be able to read in the PNGs in the normal manner.