FOPException: fo:flow must contain block-level childre

I'm in the process of doing some fairly basic XML to PDF stuff, and I'm 
getting this exception, and I'm not sure why.
I have (to summerise a much longer xsl):
...
<xsl:for-each select="report/body/section">
  <xsl:for-each select="section">
    <fo:page-sequence master-reference="main">                                                                                                                      	
    <fo:flow flow-name="xsl-region-body"> 
      <xsl:sort select="@name" order="ascending" data-type="text"/>
			<fo:block><xsl:value-of select="@name"/></fo:block>
...
    </fo:flow>
  </fo:page-sequence>
</xsl:for-each>
...

Which as far as I can tell, should work - all my blocks are in flows, in a 
page-sequence ?
Does anyone have any hints as to what might be up ?
-- 
Tom Chiverton (sorry 'bout sig.)
Advanced ColdFusion Programmer

Tel: +44(0)1749 834997
email: tom.chiverton@xxxxxxxxxxxxxx
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