Problem with IIS or PIX

I have a Win 2000 server that is running IIS5. It is hosting 3 websites and using hostheaders. Two of the sites work flawlessly. One, however, does not. If I try to browse to the site in IIS Manager, I get a site not found error. If I try to browse to it from my internal network, I also get site under construction. But, if browse to it while dialing out of my network, it comes up fine. Any suggestions?