Retrieve xml attribute value of nth xml node using xpath query

Question

I have an xml with following stucture...
<xml>
<header>
 <DocumentReference OrderId="order001">
 <DocumentReference OrderId="order002">
 <DocumentReference OrderId="order003">
I have to loop through this xml and retrieve the orderId values inside Biztalk orchestration.
In the expression shape, I get the count of 'DocumentReference' nodes using an xpath query and then
Added a loopshape to make sure it loops thru all nodes
Loop condition:   n<=nodeCount     (where n is an integer variable, n=0 to begin with, incremented by 1 thru each loop, nodeCount is # of DocumentReference nodes)
 I try retrieve to the orderId in the following expression shape using the below xpath query
  xpathQuery = System.String.Format("//*[local-name()='OrderReference'][{0}]/@orderID)",n);
  sOrderId = xpath(MsgSingleInvoice,xpathQuery);
And I get the following exception:
Inner exception: '//*[local-name()='OrderReference'][1]/@orderID)' has an invalid token.
Exception type: XPathException
Appreciate any help!   thanks!

Answer 1

Thanks for the quick response. I got rid of it.
And I see a different error:
Inner exception: Specified cast is not valid. Exception type: InvalidCastException
Source: Microsoft.XLANGs.Engine  
Target Site: System.Object XPathLoad(Microsoft.XLANGs.Core.Part, System.String, System.Type)
Since variable 'n' is of integer type, I suspected it and changed it to n.ToString() and tested again and still see the same error.