For example, a computer name of "Bob&Gina" may cause this error. In this case the ampersand is the problem.
To find the name of your computer read "What's my computer's name and address?" at http://docs.info.apple.com/article.html?path=Mac/10.4/en/mh632.html.
Note: The OS X computer name is not the same as the name of your internal hard drive.