"Not Valid Host" at GT40s.com? I had this problem, and it turned out to be an incorrect setting on Norton Internet Security. Here's the advice that fixed it for me;
I think I have the "Not Valid Host" problem sorted out for users who have Symantec's Personal Firewall / Internet Security running :
1. Open the list of Web sites:
a. Open NIS or NPF.
b. Click Options.
c. Click Internet Security or Personal Firewall. (This step is not always needed.)
d. Click the Web Content tab.
2. Add a new Web site:
a. Click Add Site. A new site/domain box appears.
b. Enter the name of the site that you want to receive the referrer information and click OK. In this example, it will be www.gt40s.com. The site name appears in the left frame of the Options window.
3. Configure the new Web site:
a. Click the name of the new site.
b. Click the Global Settings tab.
c. In the "Information about visited sites" section, clear "Use default settings".
d. Click Permit.
4. Click OK to close the Options window.
Hope this helps!