Hi Niels,

When using the 'GetXmlNodeById' function, if the content node doesn't exist, then an <error> node is returned - which is causing you the headache.

The quick fix for this is to wrap an <xsl:if> condition around the list-item, like so:

<xsl:variable name="selection" select="umbraco.library:GetXmlNodeById($frontpage/@id)" />
<xsl:for-each select="$selection/navigatiePrimair/MultiNodePicker/nodeId">
    <xsl:if test="$selection/navigatiePrimair/MultiNodePicker/nodeId != ''">
        <xsl:variable name="node" select="umbraco.library:GetXmlNodeById(.)" />
        <xsl:if test="$node[@isDoc]">
            <li>
                <xsl:if test="descendant-or-self::*[$node/@id = $currentPage/@id]">
                    <xsl:attribute name="class">current</xsl:attribute>
                </xsl:if>
                <a href="{umbraco.library:NiceUrl($node/@id)}">
                    <xsl:value-of select="$node/@nodeName"/>
                </a>
            </li>
        </xsl:if>
    </xsl:if>
</xsl:for-each>

This checks that the $node has an attribute call "isDoc" (which all content nodes have).  Otherwise it's an <error> tag and the content node doesn't exist.

Hope this helps?

Cheers, Lee.