hi,
I have changed my website to end in php and now have prblems with my left navigation sub menu's, When I hover over "About Thailand" on the following link http://www.thai-discovery.com/phuket-Thailand.php

I coped all of the li tags as follows and saved them onto a leftnav.php file

<li> <a href="#" class="vertmenu"><img src="http://www.webmaster-talk.com/images/sub menu button.png" width="12" height="8" align="right" border="none"/>About Thailand</a>
<ul>
<li><a class="vertmenu" href="Thaimonarchy.html">Thai Monarchy</a></li>
<li><a class="vertmenu" href="Thai-history.php">Thai History</a></li>
<li><a class="vertmenu" href="thai-culture.php">Thai Culture</a></li>
<li><a class="vertmenu" href="Thai-cuisine.php">Thai Cuisine</a></li>
</ul>

I replaced the above code with

<?php include_once ('incl/leftnav.php'); ?>

So why would my nav sub menu's suddenly stop working?

Firstly, don't plagiarise or hot link other website's property:

Originally Posted by TheDon

http://www.webmaster-talk.com/images/sub menu button.png

Furthermore, that file doesn't even exist.

Your website, http://www.thai-discovery.com/phuket-Thailand.php, doesn't exist either. However, http://www.thai-discovery.com/phuket-Thailand.html does exist and the sub navigation of the left-hand navigation does work for me. I am using Google Chrome 4.0.

Firstly, I did not plagiarise, it changed the link when I pasted automatically.
Secondly, I have solved the problem as I was just missing a class.

Firstly, don't plagiarise or hot link other website's property:

He didn't, the forum software has a bad habit of altering the urls to 'webmaster-talk'.