If you create multiple web sites in IIS (i.e. virtual hosts), you may see an error like this when trying to access anything other than the default web site:
Bad Request (Invalid Hostname)
For example, on the domain mm.local, we created a new web site called wiki on the collaboration server. If you tried to hit the server using the address wiki.mm.local, all would work properly. But if you tried just wiki, then you would get the exhibited error message. To correct this, open the properties page for the web site, select the Web Site tab and click the Advanced button. In the Multiple identities for this Web site section, ensure that both the long and short names for the web site are listed (e.g. both wiki.mm.local and wiki).