Typically when a web site is displaying the follow error it means that the site is not listening on the correct IP or the host headers are missing.
Bad Request (Invalid Hostname)
To access the host headers and address issues for a site follow these steps.
Start by logging into the web server where the site is hosted.
Now open up IIS Manager.
Expand the web sites folder to display all of the sites in the right hand frame.
Now right click on the domain name and select “Properties”.
The default tab is the Web Site tab, click the Advanced button next to the IP address.
This will display all the host headers for the site.
Click the “add” button to add a host header to the site. In this example we are going to add a www host header since it is missing.
Now select the same IP address as the domain is running on enter port 80 and input the www version of the domain name.
Click Ok three times and the host header should be successfully added.