Unable to transform to docbook

I have worked with C2.1 and 2.2 before. I am trying to play with C3
for a coming project.
I need to generate HTML from docbook file.

INFO  RequestProcessor - Sitemap execution for /article/ex took 6470.727 ms.
ERROR XMLSitemapServlet - Cocoon can't process the request.
org.apache.cocoon.sitemap.InvocationException:
org.apache.cocoon.pipeline.ProcessingException: Can't parse url
connection file:/home/mansour/workspace/pipelines/repo/articles/ex.xml
        at org.apache.cocoon.sitemap.util.ExceptionHandler.getInvocationException(ExceptionHandler.java:39)
        at org.apache.cocoon.sitemap.node.PipelineNode.handleException(PipelineNode.java:101)
        at org.apache.cocoon.sitemap.node.PipelineNode.invoke(PipelineNode.java:71)
        at org.apache.cocoon.sitemap.node.AbstractSitemapNode.invoke(AbstractSitemapNode.java:96)
        at org.apache.cocoon.sitemap.node.PipelinesNode.invoke(PipelinesNode.java:49)
        at org.apache.cocoon.sitemap.node.AbstractSitemapNode.invoke(AbstractSitemapNode.java:96)
        at org.apache.cocoon.sitemap.node.Sitemap.invoke(Sitemap.java:42)
        at org.apache.cocoon.servlet.RequestProcessor.invoke(RequestProcessor.java:233)
        at org.apache.cocoon.servlet.RequestProcessor.sendSitemapResponse(RequestProcessor.java:290)
        at org.apache.cocoon.servlet.RequestProcessor.service(RequestProcessor.java:90)
        at org.apache.cocoon.servlet.XMLSitemapServlet.service(XMLSitemapServlet.java:47)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

.....

Caused by: org.apache.cocoon.pipeline.ProcessingException: Can't parse
url connection file:/home/mansour/workspace/pipelines/repo/articles/ex.xml
        at org.apache.cocoon.sax.util.XMLUtils.toSax(XMLUtils.java:117)
        at org.apache.cocoon.sax.component.XMLGenerator$URLGenerator.execute(XMLGenerator.java:385)
        at org.apache.cocoon.sax.component.XMLGenerator.execute(XMLGenerator.java:104)
        at org.apache.cocoon.pipeline.AbstractPipeline.invokeStarter(AbstractPipeline.java:146)
        at org.apache.cocoon.pipeline.CachingPipeline.execute(CachingPipeline.java:143)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:601)
        at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
        at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:80)
        at org.apache.cocoon.servlet.collector.ResponseHeaderCollector.interceptInvoke(ResponseHeaderCollector.java:94)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:601)
        at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
        at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
        at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
        at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:89)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
        at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
        at $Proxy27.execute(Unknown Source)
        at org.apache.cocoon.sitemap.InvocationImpl.execute(InvocationImpl.java:141)
        at org.apache.cocoon.sitemap.node.PipelineNode.invoke(PipelineNode.java:66)
        ... 60 more
Caused by: org.xml.sax.SAXException: java.lang.NullPointerException
javax.xml.transform.TransformerException: java.lang.NullPointerException
        at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerHandlerImpl.endDocument(TransformerHandlerImpl.java:245)
        at org.apache.cocoon.xml.sax.AbstractSAXPipe.endDocument(AbstractSAXPipe.java:58)
        at org.apache.cocoon.sax.AbstractSAXTransformer.endDocument(AbstractSAXTransformer.java:47)
        at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endDocument(AbstractSAXParser.java:742)

......

Here's my pipeline:

  <map:pipelines>
        <map:pipeline>

            <map:match pattern="article/{id}">
                <map:generate
src="/home/mansour/workspace/pipelines/repo/articles/{map:id}.xml" />
                <map:transform
src="/home/mansour/workspace/pipelines/docbook-xsl-snapshot/html/docbook.xsl"
/>
                <map:serialize />
            </map:match>


This matcher is working with another transformation.
For example the following pipeline:

        <map:pipeline>

            <map:match pattern="article/{id}">
                <map:generate
src="/home/mansour/workspace/pipelines/repo/articles/{map:id}.xml" />
                <map:transform src="sheets/myCustomSheet.xsl" />
                <map:serialize />
            </map:match>

Would work fine.

The same file "ex.xml" can be processed with xalan from the command
line and produce the correct output !

any idea ??