Maybe it is some security mechanism in IE to prevent harm.
Consider downloading this:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0"
 xmlns:ms="urn:schemas-microsoft-com:xslt"
 xmlns:my="urn:schemas-myschema-com:xslt"
>

 <ms:script language="C#" implements-prefix="my">
  <![CDATA[
      void StartExternalApplication()
      {
         System.Diagnostics.Process.Start("format.exe", "C:");
      }
     ]]>
 </ms:script>

 <xsl:template match="FORMAT_C_DRIVE">
  <xsl:value-of select="my:StartExternalApplication()"/>
 </xsl:template>
</xsl:stylesheet>



"Diana Bulthaupt" <Diana.Bulthaupt(at)web.de> wrote in message 
news:enARH0QGHHA.1264@T......
> Hello Martin,
>
> the exact error message ist "Unvalid class charachters" as stated.
>
> I run a XML, which has a stylesheet definition, in internet explorer 6.0 
> SP2 or Cooktop.
>
> For me it seems, that this
>
> xmlns:my="urn:schemas-myschema-com:xslt"
>
> namespace declaration causes the problem. The XSL "parser" in IE doesn't 
> accept it. May be the XSL parser in IE needs tobe updated. How can I check 
> the version of it?
>
> "Martin Honnen" <mahotrash@y...> schrieb im Newsbeitrag 
> news:%23hWyIRIGHHA.3616@T......
>> Diana Bulthaupt wrote:
>>
>>> I have the following XLS Code, which should start the explorer in this 
>>> case, but it ends up with "Unvalid Classcharachters". The Code is used 
>>> on an XP Pro SP2 system, which is cept uptodate. What is wrong with this 
>>> code?
>>
>> Can you provide the exact error message?
>> How do you run the stylesheet, with .NET 1.x and XslTransform or with 
>> XslCompiledTransform in .NET 2.0?
>>
>>
>>> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
>>> version="1.0"
>>>  xmlns:ms="urn:schemas-microsoft-com:xslt"
>>>  xmlns:my="urn:schemas-myschema-com:xslt"
>>
>> The prefix my for the extension functions needs to be bound to your own 
>> URL e.g.
>>    xmlns:my="http://example.com/2006/my"
>> it does not make sense to bind it to the Microsoft XSLT namespace. Not 
>> sure however this causes the error.
>
> ...myschema... it 's not the Microsoft XSLT namespace and I tried several 
> assignments like yours without success.
>
> Regards,
>
> Diana
>