What would stop a simple link from working just because www. was not used before the

[Line]

What would stop a simple link from working just because www. was not used before the domain name?

Example:
http://dreamstreetms.org/
left menu doesn't work

http://www.dreamstreetms.org/
left menu works here.

Thanks ahead for your reply
-Line

[Fang]

No all domains are setup to accept the URL without www
http://no-www.org/