embedded links in Rise--two questions

1. I am trying to embed a URL using the Multimedia /Embed block.  I get an error: "We are unable to generate an embed for this URL. Please check that the URL is valid and the content is publicly accessible."  It is not publically accessible as it requires log on to access that page.  It does, however, work when I paste that same link into Interactive/button block.  Wondering why it poses a problem for the multimedia/embed and not the button.... (I'm happy it works with the button, but I'd prefer it to be simply embedded as the button opens another frame).

2. Can one specify the size of the new page that is opened by the button link?  And specify whether it is a new window vs new frame?

Thanks.