I have two sites [external links are visible to admins only] and [external links are visible to admins only]
The first indexes fine using the free generator, the second reports an error. The first is a full domain hosted by the registrar of the domain, the second is registered with a different registrar and forwarded to a subfolder of the first.
I think this error is probably linked to the cottage site's inability to register in Google. Using their webmaster tools I found that I had robots.txt in the top level site restricting acccess to the cottage one, but even though I've removed that restriction Google, and your tool, both seem unable to crawl the cottage site.
Is there some other thing I have to change? Unfortunately your error page just says "an error", not which error. Perhaps that would be a nice enhancement ...?