A Google Webmaster Help thread has one webmaster who says the fetch and render feature within Google Webmaster Tool's Fetch as Google, shows an "Error" message without any reason.
After much back and forth in the forums, Google's John Mueller said the error is with Google and not the site. John said that it looks like an "issue on our side, and not something you need to fix on your site." John said the team is aware of it and they hope to resolve it.
I am not sure if it has to do with this specific site, that the URLs are on appspot.com or if there is some other issue. I am not sure if it is an issue with one or many sites. But any Google bug that may be impacting other sites, on the reporting end, I want to let you know of.
Here is a picture of the error:
Forum discussion at Google Webmaster Help.
