fop - internal link

I have the following .fo output.

<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
<fo:layout-master-set>
<fo:simple-page-master master-name="A4" page-height="21cm"
page-width="29.7cm"  margin-top="1cm" margin-bottom="2cm" margin-left="1cm"
margin-right="1cm">
<fo:region-body margin-top="1cm"/>
</fo:simple-page-master>
</fo:layout-master-set>
<fo:page-sequence master-name="A4">
<fo:flow flow-name="xsl-region-body">
<fo:block space-before="5pt" space-after="5pt">Summary of
Accounts</fo:block>
<fo:block></fo:block>
<fo:table>
<fo:table-column column-width="3cm"/>
<fo:table-body>
<fo:table-row>
<fo:table-cell>
<fo:block font-family="sans-serif" font-size="10pt"
space-before.optimum="5pt"  space-after.optimum="5pt"><fo:basic-link
internal-destination="ACC1"
color="blue">70171234</fo:basic-link></fo:block>
</fo:table-cell>
</fo:table-row>
<fo:table-row>
<fo:table-cell>
<fo:block font-family="sans-serif" font-size="10pt"
space-before.optimum="5pt"  space-after.optimum="5pt"><fo:basic-link
internal-destination="ACC3"
color="blue">70171235</fo:basic-link></fo:block>
</fo:table-cell>
</fo:table-row>
</fo:table-body>
</fo:table>
<fo:block id="ACC1" break-before="page" space-before="5pt"
space-after="5pt">Account  Details</fo:block>
<fo:table space-after="10pt" border-after-style="solid"
border-after-width="1pt">
<fo:table-column column-width="2.5cm"/>
<fo:table-body>
</fo:table-body>
</fo:table>
<fo:block id="ACC3" break-before="page" space-before="5pt"
space-after="5pt">Account  Details</fo:block>
<fo:table space-after="10pt" border-after-style="solid"
border-after-width="1pt">
<fo:table-column column-width="2.5cm"/>
<fo:table-body>
</fo:table-body>
</fo:table>
</fo:flow>
</fo:page-sequence>
</fo:root>

When I process it with fop I get the error: 
FOP 0.20.1
using SAX parser org.apache.xerces.parsers.SAXParser
building formatting object tree
setting up fonts
 [1] [2ERROR: The id "ACC3" already exists in this document

Can anyone tell me what I am doing wrong?

Regards
	Jan





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