Render Error - Glitchy Product

Hi,

I'm getting a error message that doesn't tell me how to correct the issue. See the screen shot below.

I'm also struggling with projects not sharing between desktop & mobile, but I've just accepted that this just doesn't work.  (mobile (android) app says there's no internet connect, when there is).

Also, I start a new project in the desktop (windows 10) and the video preview is all black. This seems to be a know issue and I need to sync all of the files on to the creative cloud. 

It all feels very clunky for a product designed to be quick. But that's not my burning issue.

Can one explain how I get around this export issue?

Thanks

Gavin