Error The processing instruction target matching xX mM lL is not allowed

Question

An error occurs when I run I run an XSLT page.

The page begins as follows :

<?xml version="1.0" encoding="windows-1256"?> 
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:include href="../header.xsl"/>
  <xsl:template match="/">
    <xsl:call-template name="pstyle"/>
    <xsl:call-template name="Validation"/>
    <xsl:variable name="strLang">
      <xsl:value-of select="//lang"/>
    </xsl:variable>
    <!-- ////////////// Page Title ///////////// -->
    <title>
        <xsl:value-of select="//ListStudentFinishedExam.Title"/>
    </title>

This is the error that I am getting :

 The processing instruction target matching "[xX][mM][lL]" is not allowed

Can someone help me solve this error?