I have now 4 blogs where this error occurs constantly.
2 of them are wordpress blogs hosted on wordpress.com and 2 are blogspot blogs hosted on blogspot.*
http://chalicecarling.blogspot.de/feeds/posts/default
http://beatriceserendipity.blogspot.co.uk/feeds/posts/default
http://untouchablelife.wordpress.com/feed/
http://josiedecuir.wordpress.com/feed/
As I don't have problems with other blogs hosted on wordpress or blogspot this really puzzles me.