then it is probably because the code for the swfobject functions cannot be found. This is most likely caused by not including a link to the swfobject script in the head of the HTML page.

<script type="text/javascript" src="js/swfobject.js"></script>

Not including the code means that the object and embed tags for the player cannot be written into the HTML document at runtime.

Another possible cause is that there is an error in the path to the player SWF file, usually named "player.swf".

In this case the object embed code will be written into the HTML, but the player file is not where the code expects it to be, so it doesn't display.

In the example shown below, two players should be showing up in the second row of the table. Firebug is open to show the generated source. ( in other words all the HTML that was written to the page by javascript at runtime. It appears that the code for the player was indeed written to the page, yet still the player does not show up. So this means that swfobject did perform its function, but something went wrong after the code was written to the page.

Jeroen Wijering explains this issue quite well on his site:

Note that the Flash plugin checks for image and MP3 files relative from the HTML page and for FLV files relative from the SWF file!

Second, a playlist should always reside on the same server as the SWF file, due to security restrictions of the Flash Player. This can be solved if you own the domain on which the mediafiles reside. You then have to put a crossdomain.xml file in the root webfolder of that server. In this file, you can specifically allow sites to load data. An example is the crossdomain file from Youtube.

Checking the code in Firebug will reveal that the object code is indeed there on the page. No javascript errors will occur.

Player on left has:
"/media/playlist3.xml"
Player on right has:
"media/playlist3.xml"

Sometimes the last few tags in the playlist file may get overwritten. Try validating your XML in Dreamweaver or whatever you prefer to use.
In the example below there are several missing closing tags at the bottom:

<?xml version="1.0" encoding="utf-8"?>


<playlist version="1" xmlns="http://xspf.org/ns/0/">


<trackList>


<track>


<title>Magnetic Resonance Safety</title>


<location>02_Presentation</location>


<type>rtmpt</type>


<image>media/posterframevid20.jpg</image>