FOP error for section.autolabel option

While producing a pdf rendition from a fo file using fop 0.20.5rc2 I get the error 

[ERROR] org.apache.fop.layout.LineArea$Leader

(see below) if I specify 

<xsl:param name="section.autolabel"           select="1"/>

in my xsl customization. The page on which the error occurs seems to be the start of the TOC.

Thanks for any help with this,

Ekkehard

java -cp "c:/prog/fop-0.20.5rc2/build/fop.jar;c:/prog/fop-0.20.5rc2/lib/batik.jar;c:/prog/fop-0.20.5rc2/lib/xalan-2.4.1.jar;c:/prog/fop-0.20.5rc2/lib/xercesImpl-2.2.1.jar;c:/prog/fop-0.20.5rc2/lib/xml-apis.jar;c:/prog/fop-0.20.5rc2/lib/avalon-framework-cvs-20020806.jar;c:/prog/fop-0.20.5rc2/lib/logkit-1.0.jar;c:/prog/fop-0.20.5rc2/lib/JimiProClasses.jar;c:/prog/sgml/stylesheets/docbook-xsl-1.60.1/extensions/xalan2.jar" org.apache.fop.apps.Fop collect.fop ../pdf/collect.pdf

[INFO] Using org.apache.xerces.parsers.SAXParser as SAX2 Parser

[INFO] FOP 0.20.5rc2

[INFO] Using org.apache.xerces.parsers.SAXParser as SAX2 Parser

[INFO] building formatting object tree

[INFO] setting up fonts

[INFO] [1]

[INFO] [2]

[INFO] [3]

[INFO] [4 (blank)]

[INFO] [5]

[ERROR] org.apache.fop.layout.LineArea$Leader