I thought I’d share this experience just in case anyone else has the same problem and (hopefully) to save them valuable time.
I’ve been building my first game over the last 6 months (had to learn to programme plus FT work) and finally got to the point of having a build I wanted to put onto a device having relied on the Win simulator to that point. I tested the game in the simulator on my Mac and it worked without problems (except a font issue but that’s another story).
When I came to build however although the process worked, the app would not run on my devices (Ipad 4 & 5 and iPhone 4 & 5) and Corona was flagging a bunch of warnings about not being able to find icons (see attached). I could also see in the console also that the app was crashing at the point of loading an image.
I assumed it was my fault - as a novice - and repeated the process of creating an app, creating a provisioning profile, building etc several times with no success. I then tested it with the Corona Hello World example and got the same error.
Long story short…I was relying on Dropbox to keep my files consistent across my PC and my Mac and, now I realize, that for some reason, building from a Dropbox folder - even though the files are all local to the Mac - has some problem in relation to image file access permissions.
As soon as I copied the dir with my project files to the Mac Documents folder the build worked fine, icons are showing and I have played my game on my iPad for the first time.
I cant explain precisely why using a Dropbox folder causes the issue…but it does. So don’t do what I did 
I lost a precious day but hey…lesson learned.
…now to work out why the text isnt displaying.