Why can I not have  <xsl:analyze-string> in <xsl:template>

When I try and transform my data with my stylesheet I get the error:

"Keyword xsl:template may not contain xsl:analyze-string"

My template looks like this:

<xsl:template name="CheckValid">        
  <xsl:param name="Textstr"/>
  <xsl:param name="Expression"/>
  <xsl:param name="Replacestr"/>
   <xsl:param name="Type"/>
    <xsl:analyze-string select="$Textstr" regex="$Expression">
          <xsl:matching-substring>
              <xsl:choose>
                 <xsl:when test="$Type = 'date'">
                      <xsl:call-template name="InternationalizeDate">
                         <xsl:with-param name="Datestr" select="$Textstr"/>
                      </xsl:call-template>
                 </xsl:when>
                 <xsl:otherwise>
         <xsl:value-of select="$Textstr"/>    
                 </xsl:otherwise>
              </xsl:choose>
            </xsl:matching-substring>
            <xsl:non-matching-substring>
                <xsl:value-of select="$Replacestr"/>      
            </xsl:non-matching-substring>
         </xsl:analyze-string>
       </xsl:template>

The InternationalizeDate template is as follows:

<xsl:template name="InternationalizeDate">
  <xsl:param name="Datestr"/>
       <xsl:value-of select="concat(substring($Datestr, 7, 4), '/', substring($Datestr, 4, 2), '/',
                                  substring($Datestr, 1, 2))"/>
</xsl:template>    

and finally I call my CheckValid template as follows:

<DateofBirth>
<xsl:if test="normalize-space(Cell[12]/Data) != ''">                  
  <xsl:call-template name="CheckValid">                  
      <xsl:with-param name="Textstr" select="Cell[12]/Data"/>            
     <xsl:with-param name="Expression" select="$dateregexp"/>            
     <xsl:with-param name="Replacestr" select="''"/>
     <xsl:with-param name="Type" select="date"/>                  
  </xsl:call-template>                  
</xsl:if>
</DateofBirth>

Finally the dateregexp param is defined as follows:
<xsl:param name="dateregexp" select="'([0]?[1-9]|[12][0-9]|3[01])[-/ .]([0]?[1-9]|1[012])[-/ .](19|20)\d\d'"></xsl:param>
      
Can anyone see what I am doing wrong?  I have defined my stylesheet as using version 2.0.

Any help much appreciated.
Thanks
Sam