If you took 30 seconds to look on the Metasploit site, you'd see this:

If you are trying to use the official demo server at
metasploit.com, this will be the case (we dont want to run exploits for
random people off the internet). If you aren't running your own msfweb
server, please do so (MSFWeb in the start menu on Windows or
just 'msfweb' on Unix).
In other words, you can't be a tool and run exploits from their web demo host so stop it.

--Th13