Render Video - Quicktime Disabled

I'm in the render video dialog and quicktime option is disabled.

It wasn't a little while ago when I was playing.

I can not find in the help topics why.

Might somebody be able to help me un-disable it?

Thanks
Mathias

The render video option is greyed out when your file is flattened. It requires more than 1 layer for it to be active.