I solved the problem with the menu navigation, but I used a different approach.
I declared a property on my StartPage documenttype and added a content-picker property that is called MainMenuRoot.
I then modified my XSLT to the following
Code:<xsl:param name="currentPage"/>
<xsl:param name="rootPage" select="umbraco.library:GetXmlNodeById($currentPage/ancestor-or-self::node [string(data[@alias='MainMenuRoot'])!=''] [position()=last()] /data[@alias='MainMenuRoot'])/node" />
<xsl:template match="/">
<ul class="ul">
<xsl:for-each select="$rootPage">
<li>
LINK GOES HERE
</li>
</xsl:for-each>
</ul>
</xsl:template>
I have no idea if this is a good solution, but at least it works :)