Using #Include in htm pages

I have a .htm file in which I have the following line of code:

The htm pages are both part of my VI6 project.The file IncludeLeftPanel.htm contains only simple HTML statements as I am including my navigation definitions as an alternative to using frames.

Problem: The content in the file IncludeLeftPanel.htm is not being “included” – in fact, this line of code is being treated as a comment. Is there a setting that I have missed to enable the correct processing of this include statement? I have tried renaming the including file to have either the .shtm or .shtml suffixbut VI6 doesn’t like it.