Export Menu Item is Ghosted / Disabled

I can preview my site int he browser just fine.

But when I go to export it the Export menu is disabled.

What have I done?

Have you quit and gone back in?

Yes I have quit and gone back in.

I have solved the problem by saving to a dropbox folder. Driving home from the office and loading the project on my mac at home. — Think its a bug?

Sounds like it. Report it through the menu option so @Norm knows.