Through trial and error I think I have narrowed down the problem to the 
following:

Not Merchandised Errors - <xsl:value-of 
select="count(/Envelope/Message[(MessageID = $MessageTestList/root/list/item) 
and 
(bsi:MerchandisedProduct($CatalogConnectionString,Relationship/Relation/SKU))])"/>

May assumption is that

Relationship/Relation/SKU

in the context about is passed to my custom XSL function as a single node. 
Perhaps that assumption is in error. So now this is a query question. The 
format of the XML document looks like:

<Envelope>
  <Message>
    <MessageId>1234</MessageId>
    <Relationship>
         <Relation>
             <SKU>5678</SKU>
         </Relation>
    </Relationship>
  </Message>
</Envelope>

I want to make sure that the MessageID is in the first list (that is an 
XPath expression). Now I want to make sure that each SKU that is a sub set of 
the nodes that match the first XPath to be passed to the custom function. 

Is that confusing enough?

Kevin
"Kevin Burton" wrote:

> I have a transform that works on a large number of files. Every once and a 
> while I get the following exception thrown:
> 
> A first chance exception of type 'System.Xml.Xsl.XslTransformException' 
> occurred in System.Data.SqlXml.dll
> System.Xml.Xsl.XslTransformException: Cannot convert a node-set which 
> contains zero nodes or more than one node to a single node.
>    at System.Xml.Xsl.Runtime.XsltConvert.ToNode(IList`1 listItems)
>    at <xsl:template match="/">(XmlQueryRuntime 
> {urn:schemas-microsoft-com:xslt-debug}runtime, XPathNavigator 
> {urn:schemas-microsoft-com:xslt-debug}current)
>    at Root(XmlQueryRuntime {urn:schemas-microsoft-com:xslt-debug}runtime)
>    at Execute(XmlQueryRuntime {urn:schemas-microsoft-com:xslt-debug}runtime)
>    at System.Xml.Xsl.XmlILCommand.Execute(Object defaultDocument, 
> XmlResolver dataSources, XsltArgumentList argumentList, XmlSequenceWriter 
> results)
>    at System.Xml.Xsl.XmlILCommand.Execute(Object defaultDocument, 
> XmlResolver dataSources, XsltArgumentList argumentList, XmlWriter writer, 
> Boolean closeWriter)
>    at System.Xml.Xsl.XmlILCommand.Execute(IXPathNavigable contextDocument, 
> XmlResolver dataSources, XsltArgumentList argumentList, XmlWriter results)
>    at System.Xml.Xsl.XmlILCommand.Execute(IXPathNavigable contextDocument, 
> XmlResolver dataSources, XsltArgumentList argumentList, Stream results)
>    at System.Xml.Xsl.XslCompiledTransform.Transform(IXPathNavigable input, 
> XsltArgumentList arguments, Stream results)
> 
> 
> Any hints on how I might be able to isolate the input that is causing the 
> problem and maybe the line(s) in the stylesheet that are involved?
> 
> Thank you.
> 
> Kevin
>