date:format-date causing "No flow in page-sequence"

When trying to use  the following in an XSL-FO template I receive an "org.apache.fop.apps.FOPException: No flow in page-sequence" exception:
  <xsl:value-of select="date:format-date('2003-01-02T12:34:15', 'CCYY MM DD hh:mm:ss')"/>

If I remove the line, or even just replace with
  <xsl:value-of select="date:date-time()"/>
all is fine.  Any ideas?


                                  Cheers,
                                  James

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