Run the database tools under FiIe, Tools before exporting to Dropbox. Install the Dropbox app on the device and see if that helps. You could also try deleting the RM App for iOS and reinstalling it.
Thanks for the replies, further investigation seems to point to an issue with font size and or Auto-brightness. de-selecting both enabled the download from my dropbox which subsequently worked as it should. Strangely once the file was downloaded I could reselect my font size and auto brightness without it corrupting the RootsMagic display.