SSI appears in one page, not another

In the home stretch on my Dreamweaver web page (thanks for all the help so far), I find that the SSI "call" tag that summons up the navbar in my index.shtml file does not work in a different file ("Advising1"). The navbar (in a file called "navigation.html") is in the same (top) directlry as index.shtml. However, when I put "Advising1" in the same directory as the index and navigation files, the navbar appears just fine in Advising1. I thought that putting "virtual" in the SSI tag allowed the "calling" file to find the "called" file in any of the folders on the web site, but I guess I was wrong. So:
How do you correctly write the SSI tag so that a file may call an SSI file from another folder or directory?
Here is the mockup of the web page: (click on Advising -> English Advising):
http://s87217786.onlinehome.us/Englishx/
As always, thank you in advance.