nortbots.htm only appears in five cases:
1) You are testing on a disc-based website, including a FrontPage or
Expression Web disc-based web that is being browsed through a
web-server.
2) You are testing on a website that does not have server extensions
installed or running.
3) The site (or form page) was FTPed from a disc-based web, or
published using a FTP address for the destination, or published to a
file system destination including a network share or UNC address (like
\\machinename\path\webname), or to an address like C:\sitename .
Publish must be to a URL of the form
http://example.com
4) The site was correctly published, but the extensions were not
installed correctly or were mis-configured. Re-installing the
extensions may correct the problem. Some forms (example Search) may not
be supported by the server and may also show the error.
5) There is a bug associated with FrontPage98 which causes this
problem.
The most common reason, as Thomas mentioned, is using FTP to upload the
pages to the server. Using FTP may also corrupt the extensions which
will need to be repaired or re-installed.