I got the same error message and fixed it by fixing my incomplete hosts file. I submitted an entry to the FAQ, but it is still hidden until approval, so I will repeat it here, below the dashed line. Basically, the installation program was telling you that it could not find itself. The first thing I thought about was the fact that this is a brand-new installation of RedHat Linux, and the fact that I am not very expert at it. The second things I thought about was the fact that it could not find itself. That means look into the parts of the system that tell the OS who it is. One of those is the hosts file (/etc/hosts in Linux, also present in Windows and Macintosh). Basically, without the proper lines in /etc/hosts, your server is like a character in a bad soap opera, sitting up in bed in the hospital, head bandaged, asking, "Who am I?" to a backdrop of melodramatic violins.
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You create a new server and install moodle, you get past the server checks with flying colors, but then you get:
"The web address does not appear to be valid - this Moodle installation doesn't appear to be there."
after you input your installation and data directories. The
installation itself is telling you that the installation is not there,
but you know it is.
One cause of this is an incomplete hosts file (/etc/hosts on linux). The installation CD's should put the line:
127.0.0.1 localhost.localdomain localhost
in for you, since it is necessary for many programs in the OS itself.
Next, you need to add the IP address of your server, then the full server.
domain name, the machine's
nickname. For example:
192.168.0.24 probiscus.pointythings.com probiscus