Your JS is wrong. Actually, in the JS is HTML, and the HTML is calling your flash object from the wrong location.
There are 2 parts. For the first one, you just had "mast.swf", and the second had a full absolute URL. While the absolute URL will work, if you use SSL on your pages, it will give security warnings, so dropping the domain name solves that. Basically, use the full relative path in both places and it's all good:

Code:
document.write('<OBJECT classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000"');
document.write('codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,0,0"');
document.write('WIDTH="1024" HEIGHT="40" id="mast" ALIGN="left">');
document.write('<PARAM NAME=movie VALUE="/includes/templates/silverfish/images/mast.swf"> <PARAM NAME=loop VALUE=true> <PARAM NAME=menu VALUE=false> <PARAM NAME=quality VALUE=high> <PARAM NAME=bgcolor VALUE=#000000> <EMBED src="/includes/templates/silverfish/images/mast.swf" loop=true menu=false quality=high bgcolor=#000000 WIDTH="1024" HEIGHT="60" NAME="mast" ALIGN="left"');
document.write('TYPE="application/x-shockwave-flash" PLUGINSPAGE="http://www.macromedia.com/go/getflashplayer"></EMBED>');
document.write('</OBJECT>');
You probably, for compliance, should also change your JS call from
Code:
<script src="http://globalsubnet.com/includes/templates/silverfish/jscript/mast.js"></script>
to
Code:
<script type="text/javascript" src="/includes/templates/silverfish/jscript/mast.js"></script>