What does this Apache FOP error mean?

Error message

(Location of error unknown)org.apache.fop.fo.Validation Exception: Property id "_Ref191196753" previously used; id values must be unique in document.

Any ideas on what may cause this? Is it because I have a for-each and apply the same template multiple times开发者_运维百科?

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The specification states the id of an element must be unique.

The following code produces the error message you get.

<fo:block id="_Ref191196753"/>
<fo:block id="_Ref191196753"/>

You need to search your fo-file to locate the occurences of the elements with the same id. Then make changes in your XSLT to eliminate these.