XPath Error

I am having troubles using an XPath query inside of an expression shape for a received message in an orchestration. Here are the details.

XPath Query:

/*[local-name()='batch']/*[local-name()='rec'][position()='1']/*[local-name()='messageId']

This XPath query is actually from the "Instance XPath" in the Schema Editor for my XSD.

XML Document:

<?xml version="1.0"?>
<batch xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <batchId>b1</batchId>
  <rec>
    <messageId>m1</messageId>
    <data>foo</hl7_data>
  </rec>
  <rec>
    <messageId>m2</messageId>
    <data>bar</data>
  </rec>
</batch>

Exception Details:

System.InvalidOperationException: There is an error in the XML document. ---> System.InvalidOperationException: <messageId> was not expected.
at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderString.Read2_string()
--- End of inner exception stack trace ---
at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, XmlDeserializationEvents events)
at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader)
at Microsoft.XLANGs.Core.Part.XPathLoad(Part sourcePart, String xpath, Type dstType)
at DSSI.ReadyMed.PatientPayer.PCC.ServiceOrchestration.segment2(StopConditions stopOn)
at Microsoft.XLANGs.Core.SegmentScheduler.RunASegment(Segment s, StopConditions stopCond, Exception& exp)

I searched for other posts with no luck. Any assistance would be appreciated.

Thank you,
--Marcin Polewski

I figured out my problem. The XPath query need to have a surrounded "string()" function call as follows:

XPath Query:

string(/*[local-name()='batch']/*[local-name()='rec'][position()='1']/*[local-name()='messageId'])

P.S. This site is great!

Thanks,
--Marcin