There are two common errors that you can make when using Server Side Includes. First, you should not forget the "#" sign:
<!--echo var="REMOTE_USER"-->
Second, do not add extra spaces between the "-" sign and the "#" character:
<!-- #echo var="REMOTE_USER"-->
If you make either of these two mistakes, the server will not give you an error; rather it will treat the whole expression as an HTML comment.