LAMP Apache - Virtual Server - Website fails when I specify address

I am running a turnkey linux lamp install.  I have a webserver www.mydomain.com .  It works fine if I leave the address as 'any' however I want to add a second website on this server.  In advance of that I  tried putting mydomain.com and www.mydomain.com in address area but either of them cause a file not found error.  Is there something wrong with the format I am using?   If I switch it back to 'any' and restart apache it comes right back