If you are currently seeing a warning in Google Webmaster Tools that reads, "Invalid XML tag," don't worry. There are many webmasters reporting the issue and Google has confirmed it is a bug. Google said in an announcement post:
Some Blogspot / Blogger sites have reported seeing a warning "Invalid XML Tag. This tag was not recognized. Please fix it and resubmit. Parent tag: author." This message is just informational and does not affect our parsing of your RSS feed for Sitemaps, nor does it affect your site's crawling and indexing.
I personally saw this error presented on a site that was not Blogspot or Blogger on Thursday or Friday and the error is now gone.
Googler, JohnMu said:
As mentioned in the other thread, you can safely ignore this message. It's more of a warning and the URLs in your feed will still get processed normally. No need to worry :-))