Unexpected type problem

[Paul Wilson <paul@...>]

I am new to Lua and I have run into something I do not know how to 
handle.  I am converting some VB.NET code to Lua to run in a Luanet (Lua 
5.0.2) environment.  The code fragment below is supposed to take an XML 
document contained in a string and extract the inner text value for the 
XML tag <MessageContent> which is then to be analysed.  In the VB case 
the result of accessing the InnerText property of a node returns a 
string.  However, when the code containing the fragment below is run, 
the string.find call causes an exception, the description of which 
indicates that the first parameter (messageContents) is a table and not 
a string.  Can someone tell me what I am doing wrong please.

Thanks,

Paul Wilson
(paul@paulwilsonconsulting.com)

Code Fragment:

   -- Extract the message contents
   xmlDocument = luanet.import_type("System.Xml.XmlDocument");
   local document = xmlDocument();
   document:LoadXml(myMessage);

   -- Attempt to get the message content string
   local nodes = document:GetElementsByTagName("MessageContent");
   local messageContents = "";
   if nodes.Count == 0 then
  
               .
               .
               .
 
   elseif nodes.Count > 1 then
  
               .
               .
               .
 
   else
  
       -- Save the message contents
       messageContents = nodes[0].InnerText;
   end

   -- Look for multiple messages
   index = string.find(messageContents, ">");

begin:vcard
fn:Paul Wilson
n:Wilson;Paul
org:Paul Wilson Consulting
adr:;;P.O. Box 87;Seba Beach;Alberta;T0E 2B0;Canada
email;internet:paul@paulwilsonconsulting.com
title:Senior Consultant
tel;work:+1.780.951.3521
tel;fax:+1.928.396.4532
tel;home:+1.780.797.4214
tel;cell:+1.780.951.3521
url:http://www.paulwilsonconsulting.com
version:2.1
end:vcard