iOS crashing on Texture2D LoadImage

I have a problem where my app crashes on an iPod 4 while loading a texture that has been downloaded using WWW. I have a reasonably small and simple scene with a couple of dozen textures (optimised for iPhone, but possibly still quite big) and a few low poly meshes. Into this scene I load another 8 textures from the web and replace the materials on a few of the objects.

By fiddling around I managed to get the scene to load and create the texture initially, but when I return to the level it crashes, even though all of the objects are being deleted in between scenes.

The built in profiler shows that I'm only using around 10MB of System Memory - so I guess that this must be something to do with the textures. I don't really know how much texture memory I have to play with - the web player shows I have 50MB in textures.

I'm using the downloaded images to provide some decent text formatting - I could possibly reduce the numbers of textures, but if I did that I would have to use LoadImage frequently during gameplay and it appears to be pretty slow.