Hi,

This one has be properly stumped.  I've spent hours on my own and with a colleague troubleshooting this and with trial and error have been able to reproduce this on a very simple page with a simple controller, but still cannot determine the root cuase or the solution.  Any assistance would be appreciated.

The use case is ultimately a customised site for a pulic knowledge base.  One feature will be to display articles that have been marked as features using a custom picklist field on the article object.  The article type is "Support Article" so the object is support_article__kav.

Here is the controller that queries the object and returns a list of artcles that are featured:

public class TestPageController 
{
    // method to return a list of support articles that have the field Featured="Yes"
    public static list<Support_Article__kav> FeaturedArticles  {
        get {
            if	(FeaturedArticles == null) {
                FeaturedArticles = 
                    [
                        SELECT Id, KnowledgeArticleId,Title
                        FROM 
	                        Support_Article__kav
                        WHERE 
                            Featured__c 	= 'Yes' AND 
                            PublishStatus	= 'online' AND 
                            language		= 'en_US' 
                        LIMIT 10
                    ];
            }
            return FeaturedArticles;
        }
    }    
}

This is rendered on the following VisualForce page (as a simple list for purposes of illustration of the problem:

<apex:page controller="TestPageController" sidebar="false" showHeader="false" docType="html-5.0" standardStylesheets="true">
    
    <h1>Featured Articles</h1>
    <ul>
        <apex:repeat var="fa" value="{!featuredArticles}">
            <li>
                <a href="{! URLFOR($Action.KnowledgeArticle.View, LEFT(fa.KnowledgeArticleId,15)) }">
                    {!fa.title} (ID={!fa.KnowledgeArticleId}) 
                </a>
            </li>  
        </apex:repeat>
    </ul>

</apex:page>

When this page is displayed (https://c.cs17.visual.force.com/apex/test_page) it results in the following error:
Now for the very strange extension of the problem.  If I add another article list to the page using <knowledge:articleList> which displays 10 articles in similar list then the whole page (BOTH LISTS) display correctly:

<apex:page controller="TestPageController" sidebar="false" showHeader="false" docType="html-5.0" standardStylesheets="true">
    
    <h1>Featured Articles</h1>
    <ul>
        <apex:repeat var="fa" value="{!featuredArticles}">
            <li>
                <a href="{! URLFOR($Action.KnowledgeArticle.View, LEFT(fa.KnowledgeArticleId,15)) }">
                    {!fa.title} (ID={!fa.KnowledgeArticleId}) 
                </a>
            </li>  
        </apex:repeat>
    </ul>
    
    <!-- If you add the articlelist below, the page WORKS CORRECTLY. Remove it and the page fails. --> 
    <h1>All Articles</h1>
    <ul>
        <knowledge:articleList articleVar="article" pageSize="10" > 
            <li>
                <a href="{! URLFOR($Action.KnowledgeArticle.View, article.id) }">{!article.title}</a> (ID={!article.Id}) 
            </li>  
        </knowledge:articleList>
    </ul>
    
</apex:page>

The above code samples are complete and compile in my org.

I am desparate from some solution to this.

Thanks in advance
Derek