Blogger has split itself into separate country domains, such as blogspot.com for US, blogspot.co.uk for UK, blogspot.com.au for AU.
But what’s really puzzling is that these apply to the user, not the blog. The blog may be visible on a multitude of different blogspot country domains, dependent on where the user is located.
This has broken a number of addon tools, such as commenting and social networking.
More details at Girl Does Geek
How to override it (though it only lists a few of the country domains; you’d need to find as many as possible to add in to make it work for everybody)
— It rather appears that Google/Blogger didn’t think too carefully about this.
I wonder if this is why I can’t comment on Word Press blogs as of yesterday unless I change my email address.