We reported this about a week ago but it seems to have gone unnoticed. Google has officially retired support for Geo Sitemaps.
Google's Susan Moskwa said this a week ago:
Google has retired support for the Geo Sitemaps format. You can continue to submit your Geo content to us using the standard Sitemaps format (just listing the URL of the file(s), without -specific tags).
This explains why the geo sitemap XML files were returning errors in Google Webmaster Tools in February. The invalid tag is invalid because Google quietly stopped supporting them.
A Google Places Help thread has Vanessa from Google a bit confused as to why or when this happened but it did.
Google still does support the KML Files format, which you can learn about over here but not the geo sitemap format.
Forum discussion at Google Places Help.