I'm not too sure what the problem is, but it looks like no one else has either, so I'll have a go at a couple of ideas. Are you able to open the saved web page in whichever browser you use? If you can, it might be something to do with your copy of Front Page, can you try a repair to it? If it won't repair, try reinstalling it.
If you still get no joy, try taking a copy of the page off the web site and see it will let you edit it.
One last thought, is there anything one the web site that requires a connection to the Internet while your are editing it? Like external images or advertising links, it might be a problem with your firewall blocking access, try switching it off temporarily.
lastly, if you are still having a problem, are you willing to try another web page editor? I use Mozilla composer, it comes with the Mozilla suit which includes the Mozilla browser and email client, but these can be ignored if you just want to use the editor: