Can a banner created from new file be dynamic? Or do I have to use template?

[CPW]

I'm unable to use the GWD templates as I get an error message (attached screen grab) when opening. I've tried opening several different templates with no success, the folder gets created but no files.

I have created a banner from scratch, but the plus button in the dynamic panel is greyed out and I am unable to add anything.

Can anyone offer any advice? I'm working on a Mac - Yosemite 10.10.4 and have no previous experience using Google Web Designer.