LoadMovie works in Player but not in HTML

I’m publishing to Flash 8 Player and even though I can load one movie into another within Flash, when I publish the HTML all I can see is the container SWF - the loaded SWF is invisible. I’ve tried this with more than one loader movie and the result is the same. Here’s my HTML for Flash:


<script language="JavaScript" type="text/javascript">
<!--
if (AC_FL_RunContent == 0 || DetectFlashVer == 0) {
    alert("This page requires AC_RunActiveContent.js.");
} else {
    var hasRightVersion = DetectFlashVer(requiredMajorVersion, requiredMinorVersion, requiredRevision);
    if(hasRightVersion) {  // if we've detected an acceptable version
        // embed the flash movie
        AC_FL_RunContent(
            'codebase', 'http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=8,0,24,0',
            'width', '960',
            'height', '516',
            'src', 'quiz_ui',
            'quality', 'high',
            'pluginspage', 'http://www.macromedia.com/go/getflashplayer',
            'align', 'middle',
            'play', 'true',
            'loop', 'true',
            'scale', 'showall',
            'wmode', 'transparent',
            'devicefont', 'false',
            'id', 'quiz_ui',
            'bgcolor', '#ffffff',
            'name', 'quiz_ui',
            'menu', 'true',
            'allowScriptAccess','sameDomain',
            'allowFullScreen','false',
            'movie', 'swf/quiz_ui',
            'salign', ''
            ); //end AC code
    } else {  // flash is too old or we can't detect the plugin
        var alternateContent = 'Alternate HTML content should be placed here.'
            + 'This content requires the Adobe Flash Player.'
            + '<a href=http://www.macromedia.com/go/getflash/>Get Flash</a>';
        document.write(alternateContent);  // insert non-flash content
    }
}
// -->
</script>
<noscript>
    <object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=8,0,0,0" width="960" height="516" id="quiz_ui" align="middle">
    <param name="allowScriptAccess" value="sameDomain" />
    <param name="allowFullScreen" value="false" />
    <param name="movie" value="swf/quiz_ui.swf" /><param name="quality" value="high" /><param name="wmode" value="transparent" /><param name="bgcolor" value="#ffffff" />    <embed src="swf/quiz_ui.swf" quality="high" wmode="transparent" bgcolor="#ffffff" width="960" height="516" name="quiz_ui" align="middle" allowScriptAccess="sameDomain" allowFullScreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" />
    </object>
</noscript>

My LoadMovie script:


var contentMC:MovieClip = content_mc;
var displayPercent:MovieClip = loadinfo_mc;
displayPercent._visible = false;

///////////// MovieClipLoader /////////////////////
var loader:MovieClipLoader = new MovieClipLoader();
loader.addListener(this);
function onLoadInit(contentMC:MovieClip) {
    displayPercent._visible = false;
    content_mc._lockroot = true; //Doesn't see to make a difference
    //Alert.show("LOADED");
}

function onLoadProgress(contentMC:MovieClip, loaded:Number, total:Number) {
    contentMC._visible = true;
    displayPercent._visible = true;
    var percent:Number = Math.floor(loaded / total * 100);
    displayPercent.infodisplay_txt.text = "LOADING: " + percent + "%";
}
///////////// File to load immediately /////////////
externalSWF = "page1.swf";
loader.loadClip(externalSWF,contentMC);

Both files are published to Flash 8 Player and set to wmode ‘transparent’. Has anyone else encountered this problem? One other interesting note: if I set up an Alert box to appear on load, it never appears if I run the files within the HTML page, only if I run the container file within the Flash authoring environment (then everything works fine).