I selected a content tag as a service parameter instead of a page tag :

org.apache.cocoon.ProcessingException:Attempted to process incomplete pipeline.

Caused by: org.apache.cocoon.ProcessingException: Attempted to process incomplete pipeline.
at org.apache.cocoon.components.source.impl.SitemapSource.init(SitemapSource.java:380)
at org.apache.cocoon.components.source.impl.SitemapSource.<init>(SitemapSource.java:215)
at org.apache.cocoon.components.source.impl.SitemapSourceFactory.getSource(SitemapSourceFactory.java:65)
at org.apache.excalibur.source.impl.SourceResolverImpl.resolveURI(SourceResolverImpl.java:208)
at org.apache.cocoon.components.CocoonComponentManager.resolveURI(CocoonComponentManager.java:558)
at org.apache.cocoon.components.CocoonComponentManager.resolveURI(CocoonComponentManager.java:558)
at org.apache.cocoon.components.CocoonComponentManager.resolveURI(CocoonComponentManager.java:558)
at org.apache.cocoon.components.CocoonComponentManager.resolveURI(CocoonComponentManager.java:558)
at org.apache.cocoon.components.CocoonComponentManager.resolveURI(CocoonComponentManager.java:541)
at org.ametys.web.repository.FilteredContentsGenerator.generate(FilteredContentsGenerator.java:154)
at org.apache.cocoon.components.pipeline.AbstractProcessingPipeline.processXMLPipeline(AbstractProcessingPipeline.java:579)
... 55 more
Caused by: org.apache.cocoon.ProcessingException: Attempted to process incomplete pipeline.
at org.apache.cocoon.components.pipeline.AbstractProcessingPipeline.preparePipeline(AbstractProcessingPipeline.java:491)
at org.apache.cocoon.components.pipeline.AbstractProcessingPipeline.prepareInternal(AbstractProcessingPipeline.java:515)
at org.apache.cocoon.components.source.impl.SitemapSource.init(SitemapSource.java:343)
... 65 more