Some users are experiencing issues with Apple's MobileMe when attempting to publish their iWeb sites to it. MobileMe makes publishing your websites from iWeb easy with one-click, Mac OS X integrated publishing.
Apple Support Discussions user "Durandel" reports the issue:
Error: Couldn't reach the MobileMe configuration server. Try publishing again later.
Well, I tried later. 24 hours later. What's up?
Later in the thread "Durandel" offers a solution that worked for them:
Go to Finder -> HomeFolder -> Library
Move entire folder "Caches" to desktop
Restart iWeb and publish
It should work now
You can now delete "Caches" folder in desktop.
Users may also contact Apple's 24/7 MobileMe support chat if they continue to have problems. Simply choose your location and the issue you are having and an option to begin a chat will appear.