I had downloaded my archived Posterous blog backup and unzipped it. As directed, I selected the "wordpress_export_1.xml" file to import my old Posterous blog into my new WordPress blog (the file was exactly where the WordPress help page said it would be), but got the message "Sorry, there has been an error. The file is not an xml file. Please see instructions for downloading and using the Posterous backup file" This took me back to the document I'd just been at.
The blog I need help with is saracambridge.wordpress.com.