What to do if you cannot export a png of your design
What a pain! Here's a couple of gotcha's to look out for.
If you've added a background image by adding it in the CSS editor, then that will break the export feature. It's a known issue, so it's not forever, but for now just delete the background-image declaration from your CSS, hit Save and try again.
Filesize greater then 1.5Mb (Chrome only)
It doesn't sound like much but if you are using Chrome and try to export your project as a png, the browser will crash. It's not really a Typecast issue, but we are still trying to figure out a way around it. And in the mean time, you can fire up Safari and export your PNG from there, or split your project into small chunks by duplicating and removing content and/or containers.
If it's still not working, let us know.