Take another look at your error message, and you'll see that there are two errors:

The specified CGI application misbehaved by not returning
a complete set of HTTP headers.
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and...

Bareword "ONF" not allowed while "strict subs" in
use at C:\webdev\wwwroot\cgi-bin\index.pl line 37.
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The first error is coming from the server, the second error is coming from perl. The bareword error that causes perl to emit its error message is not necessarily the cause of the http headers error, and it is only referenced because the server seems to think it may have been a failed attempt to print a header.

Fixing the bareword error in your perl is not guaranteed to fix the problem with the headers. Remember that the first thing your script should print to STDOUT is an http header. If you're outputting HTML, this will usually work:

print "Content-type: text/html\n\n";
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