It looks like it happens always with rich text content. For an example (this 
is the automatically generated upgrade.xsl to a really simple Infopath form 
which consists on a rich text field alone "m:richTextField" and later added 
a new attribute "my:newAttribute").

upgrade.xsl:
--------------------------------------
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
xmlns:msxsl="urn:schemas-microsoft-com:xslt" 
xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2006-01-04T15:33:26" 
xmlns:xd="http://schemas.microsoft.com/office/infopath/2003" 
xmlns:xhtml="http://www.w3.org/1999/xhtml" version="1.0">
 <xsl:output encoding="UTF-8" method="xml"/>
 <xsl:template match="text() | 
*[namespace-uri()='http://www.w3.org/1999/xhtml']" mode="RichText">
  <xsl:copy-of select="."/>
 </xsl:template>
 <xsl:template match="/">
  <xsl:copy-of select="processing-instruction() | comment()"/>
  <xsl:choose>
   <xsl:when test="my:myFields">
    <xsl:apply-templates select="my:myFields" mode="_0"/>
   </xsl:when>
   <xsl:otherwise>
    <xsl:variable name="var">
     <xsl:element name="my:myFields"/>
    </xsl:variable>
    <xsl:apply-templates select="msxsl:node-set($var)/*" mode="_0"/>
   </xsl:otherwise>
  </xsl:choose>
 </xsl:template>
 <xsl:template match="my:myFields" mode="_0">
  <xsl:copy>
   <xsl:attribute name="my:newAttribute">
    <xsl:value-of select="@my:newAttribute"/>
   </xsl:attribute>
   <xsl:element name="my:richTextField">
    <xsl:apply-templates select="my:richTextField/text() | 
my:richTextField/*[namespace-uri()='http://www.w3.org/1999/xhtml']" 
mode="RichText"/>
   </xsl:element>
  </xsl:copy>
 </xsl:template>
</xsl:stylesheet>
-------------------------------------------

When applied to this .xml file generated with Infopath after filling the 
form (with no my:newAttribute):
form2.xml:
--------------------------
<?xml version="1.0" encoding="UTF-8"?>
<?mso-infoPathSolution solutionVersion="1.0.0.2" productVersion="11.0.6565" 
PIVersion="1.0.0.0" 
href="file:///C:\Documents%20and%20Settings\IvarZapata2\My%20Documents\Desktop\UpgradeInfopath\Template1.xsn" 
name="urn:schemas-microsoft-com:office:infopath:Template1:-myXSD-2006-01-04T15-33-26" 
?><?mso-application progid="InfoPath.Document"?><my:myFields 
xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2006-01-04T15:33:26" 
xml:lang="es">
 <my:richTextField>
  <div xmlns="http://www.w3.org/1999/xhtml">Rich text content</div>
  <div xmlns="http://www.w3.org/1999/xhtml"></div>
 </my:richTextField>
</my:myFields>
-------------------------

The program I use is really simple:

using System;
using System.Xml;
using System.Xml.XPath;
using System.Xml.Xsl;

class QuickXslTransformer
{
 private XslTransform xslt = new XslTransform();

 public QuickXslTransformer(
  string source,
  string stylesheet,
  string output)
 {
  xslt.Load(stylesheet);
  xslt.Transform(source, output, null as XmlResolver);
 }


 /// <summary>
 /// The main entry point for the application.
 /// </summary>
 [STAThread]
 static void Main(string[] args)
 {
  try
  {
   QuickXslTransformer o;
   o = new QuickXslTransformer(args[0], args[1], args[2]);
  }
  catch (Exception e)
  {
   Console.WriteLine(
    "Unable to apply the XSLT transformation.");
   Console.WriteLine("Error:\t{0}", e.Message);
   Console.WriteLine("Exception: {0}", e.GetType().ToString());
   Console.ReadLine();
  }

  return;
 }
}




"Martin Honnen" <mahotrash@y...> wrote in message 
news:OgrFzLTEGHA.1180@T......
>
>
> IvarZap wrote:
>
>> That's the message. However, in the stylesheet there is no namespaceuri() 
>> function but only namespace-uri().
>>
>> One more data. If I transform with the msxsl.exe program it works fine.
>>
>> Is this a bug of System.Xml.Xsl?
>
> Try to reduce the stylesheet to the minimum and post it or at least show 
> us relevant excerpts so that we can check what the stylesheet does and for 
> which kind of function call you get the error message.
>
> -- 
>
> Martin Honnen --- MVP XML
> http://JavaScript.FAQTs.com/