XPath Query on Distincit Values Problem

Dear Friends
I have some problems to get the distinct values from an XML
----------------------------
<Test1>
      <MetadataEntity>
            <AccountID>1</AccountID>
            <OrganizationCode>12</OrganizationCode>
            <ClientName>VRK Trusts</ClientName>
      </MetadataEntity>
      <MetadataEntity>
            <AccountID>1</AccountID>
            <OrganizationCode>14</OrganizationCode>
            <ClientName>GK Logistics</ClientName>
      </MetadataEntity>
      <MetadataEntity>
            <AccountID>1</AccountID>
            <OrganizationCode>14</OrganizationCode>
            <ClientName>VRK Trusts</ClientName>
      </MetadataEntity>
      <MetadataEntity>
            <AccountID>1</AccountID>
            <OrganizationCode>14</OrganizationCode>
            <ClientName>GK Logistics</ClientName>
      </MetadataEntity>
</Test1>

------------------
I want to get the distinct Client names for account id 1 and organization code

I used the follwing XPath Query
      /Test1/MetadataEntity[AccountID = 1 and OrganizationCode = 14 and ( not ( ClientName = preceding-sibling::MetadataEntity/ClientName))]/ClientName

It doesnot successful
I get only "GK Logistics" I did not get "VRK Trusts"

I think VRK Trusts was found on the first node and the query skips it.???

Help Me on this plz....

My Code in .NET C#
--------------------------
            XPathDocument xPathDoc = new XPathDocument(@"E:\Test1.xml");
            XPathNavigator xnav = xPathDoc.CreateNavigator();
            XPathExpression expression = xnav.Compile("/Test1/MetadataEntity[AccountID = 1 and OrganizationCode = 14 and ( not ( ClientName = preceding-sibling::MetadataEntity/ClientName))]/ClientName");

            expression.AddSort(".", XmlSortOrder.Ascending, XmlCaseOrder.None,
                  "", XmlDataType.Text);
            XPathNodeIterator iterator = xnav.Select(expression);

            while (iterator.MoveNext())
            {
                  XPathNavigator nav2 = iterator.Current.Clone();
                  MessageBox.Show(nav2.Value);//iterator1.Current.Value);
            }
--------------------------

regards
prakashStart Free Trial