When I upload files to LR4 from Dropbox (Camera upload from Sony Xperia Z3 Compact) about half the previews are Green & pink instead of their actual colours, and this occurs randomly through the downloaded set. When i click on the thumbnail for a full size view the colours correct themselves but still remain pink/green in the previews. Why is this and what can I do about it?
The initial preview you see is taken from the jpeg preview embedded in the presumably raw files. After a while or when you click on the file Lightroom generates its own preview. So it sounds like something is wrong with the embedded jpegs. You can have Lightroom generate standard previews by selecting all files you imported and going to the Library->Previews menu item.
Perfect... Thank you!