Make sure you have the latest Chrome version. An earlier update had problems with Web Apps.
See this page also and this Jot Form converted to a Web App
Web App converted from a Google Mouseover Gadget.
For the Tip of the Day code I converted this gadget code to a Web App. Note clicking the link will download the gadget code to your computer.
I use the code from here and created a Web App for the image popup below.