[BRotondi]

O.K. solved this, but really don't know, what's causing it, since the template mediawiki_navbar_link ist the same on my working XAMPP and my buggy server-installation. Perhaps if you install vbMediaWiki on 4.0.2 and then update to .3 something will be updated, which interprets above template in another way...

Solution: replace those vars with the new {}-descriptors: Change mediawiki_navbar_link to

<vb:if condition="$vboptions['selectednavtab'] == 'vbmediawiki'">
<li class="selected">
    <a class="navtab" href="{vb:raw vboptions.mediawiki_path}">{vb:raw vboptions.mediawiki_name}</a>
    <ul class="floatcontainer">
{wiki:raw personal_urls}
    </ul>
</li>
<vb:else />
<li>
    <a class="navtab" href="{vb:raw vboptions.mediawiki_path}">{vb:raw vboptions.mediawiki_name}</a>
</li>
</vb:if>

For those who want to install vbMediaWiki on a 4.0.3, you can directly use the new xml which has above changes included (Attachement).