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If you are using the Frontpage publishing routine and don't have server extensions installed, install them from your control panel or ask your host to do it.
If you are using the Frontpage publishing routine and [i]have[i] FP server extensions installed, go to your control panel and see if there's an entry to "Repair" the extensions. Give that a shot. If that doesn't do it, first "uninstall" then reinstall the extensions (or ask your host).
But...it actually sounds like you're trying to FTP the files with Frontpage. That could go back to a firewall problem or a permissions problem or something just hinky on the server. If anything above doesn't clear it up you'll probably have to contact them.