I've followed the steps you describe for importing an XML file generated by the Posterous backup function, but WordPress is refusing to import it. When I try, it gives me an error message reading:
Sorry, there has been an error.
Could not read the XML file. Please make sure you are uploading a valid .xml or .xml.gz file. For more info, please see our documentation.
The blog I need help with is solchrom.wordpress.com.