If you get this error when you try and publish your website with iWeb to your FTP server;
"There was an error communicating with the FTP server. Try again later, or check with your service provider"
It is due to a bug in iWeb. It is caused when you try an add an image, video or other media file to your website that begins with a space character. You can either try to find the offending file(s) and replace them, or use <a href="http://www.ragesw.com/products/iweb-seo-tool.html">iWeb SEO Tool</a>, free with one year or more of web hosting, to publish your website.
This video explains the problem in more detail and exactly how to fix it;