After uploading my sitemap.xml file to Google Webmaster Tools I received the following error message and no additional error details were included:
Error: The last attempt at downloading the Sitemap failed. The details below are representative of the last successful download.
I searched around a bit and found a forum post where someone said they get this error 'sometimes', but after switching to use a gzip formatted sitemap.xml file the error went away
compresses the file to ./sitemap.xml.gz and deletes the sitemap.xml file by default
after uploading Google was able to process without issue