This issue is caused by an ID token stored in your web browser that is passed between Wavve and The Editor.
To resolve this issue, the token needs to be refreshed. Follow these steps:
1) Ensure that you are using Google Chrome as your browser (this is the browser with the best support for Wavve)
2) Log out of Wavve
3) Close ALL open Chrome Tabs
4) If you are using Windows as your Operating System, open the Task Manager and ensure all Google Chrome processes are closed. This walkthrough guide will show you how to do this.
If you are using a Mac, force close the Google Chome application. This walkthrough explains how to do this.
5) Open Chrome
6) Log in to Wavve and attempt to create & save a design
If the above steps do not resolve the issue, log out of Wavve and restart your computer. Then log in to Wavve and try again.