This post expands upon the post made a while back on Server Side Includes (SSI) and .shtml Pages. I was recently tinkering with SSI and was attempting to include an HTML file located in the parent directory of a certain SHTML file. Using <!--#include file="../file.html"--> does not work for this. The following code which uses the "virtual" argument must be used instead:

<!--#include virtual="../file.html" -->

The virtual argument can also be used in any situation where the file you are including is located in a position requiring an address starting at the server root.

<!--#include virtual="/directory/included.html" -->