I've just run the homepage of a site I'm working on through the w3c HTML validator and it's come back with 3 errors and 2 warnings. I've taken a look at them but can't see why they would be causing a problem. I've pasted them in below (I've removed URL's/strings etc as the site isn't quite ready to be made public yet). This is being validated against XHTML Transitional by the way.

The UL comes back with the following error: end tag for "ul" which is not finished <ul id='tabs'></ul>

<ul id='tabs'> 
<li> 
    <a href="/en/folder/folder/search?categories[]=cat1" class="tab1" title="tab_title">
        <img alt="img_alt" src="img_src" /> 
        <span> 
            tab1_text
        </span> 
    </a>
</li> 
<li> 
    <a href="/en/folder/folder/search?categories[]=cat2" class="tab2" title="tab_title">
        <img alt="img_alt" src="img_src" /> 
        <span> 
            tab2_text
        </span> 
    </a>
</li> 
<li> 
    <a href="/en/folder/folder/search?categories[]=cat3" class="tab3" title="tab_title">
        <img alt="img_alt" src="img_src" /> 
        <span> 
            tab3_text
        </span> 
    </a>
</li> 
<li> 
    <a href="/en/folder/folder/search?categories[]=cat4" class="tab4" title="tab_title">
        <img alt="img_alt" src="img_src" /> 
        <span> 
            tab4_text
        </span> 
    </a>
</li> 
<li> 
    <a href="/en/folder/folder/search?categories[]=cat5" class="tab5" title="tab_title">
        <img alt="img_alt" src="img_src" /> 
        <span> 
            tab5_text
        </span> 
    </a>
</li> 
<li> 
    <a href="/en/folder/folder/search?categories[]=cat6" class="tab6" title="tab_title">
        <img alt="img_alt" src="img_src" /> 
        <span> 
            tab6_text
        </span> 
    </a>
</li> 
<li> 
    <a href="/en/folder/folder/search?categories[]=cat7" class="tab7" title="tab_title">
        <img alt="img_alt" src="img_src" /> 
        <span> 
            tab7_text
        </span> 
    </a>
</li> 
<li> 
    <a href="/en/folder/folder/search?categories[]=cat8" class="tab8" title="tab_title">
        <img alt="img_alt" src="img_src" /> 
        <span> 
            tab8_text
        </span> 
    </a>
</li> 
</ul>

For the inline javascript, I'm getting 2 errors and 2 warnings all for the same thing - I have a simple if statement with && and the validator appears to be seeing this as HTML rather than javascript: character "&" is the first character of a delimiter but occurred as data and xmlParseEntityRef: no name

<script type='text/javascript'>
    if (weather_data != null && weather_data['data'] != null){
    display_weather();
}
</script>

The javascript is placed just before the body close tag at the end of the document. If you need to see the full source then let me know and I can send it over.