Per the FAQ, you’ll find error codes always in the page source rather than publicly displayed.
Typically the plugin doesn’t embed Google Documents – I know, that makes the plugin seem like a misnomer. If you save your file to your own web site and link to it there, it will work. You can try to embed it from Google Docs itself, but this is temperamental at best. You’ll have to add force=”1″ to the shortcode to bypass the file type check, or turn off internal error checking for all docs under GDE Settings/Advanced.
It’s called Google Doc Embedder because it uses the viewer from Google Docs as a standalone viewer for (typically locally hosted) file types. There is no native connection to Google Docs service itself, as I’ve never been able to reliably use the viewer for this service (ironically).