Funny story, we worked on the iPhone app for thousands of hours and at the last moment introduced a bug that caused all new users that had not installed the app previously to be unable to see the demo. We submitted an update request to Apple last Tuesday and have finally got the update pushed through.
So, if you have had any issues with the app not allowing you to write or seeming unresponsive, un-install the app from your device, and reinstall it from the App store and the problems should now be resolved.
If the app worked for you hunky-dorey the first time, no need to uninstall, you're good to go. The app store will tell you to update the app, but there's only one fix in the update which is described above.
Thanks everyone for your patience and incredible understanding!