FOP 0.15 and Cocoon

[Stefano Angelici <s....@elogic.it>]

Hi everybody. I've got cocoon 1.8 installed in a server. Cocoon had
fop_0.13 as PDF render library; now I put fop_0.15 and w3c.jar(I deleted
the previous fop symbolic link and created a new one) in tomcat/lib. I
tryed to create a PDF (from xml and xsl files) using XalanCommandLine in
command line and everything works, but as I recall the same script using
Netscape fop creates this error:

java.lang.NullPointerException: 
	at java.util.Hashtable.get(Hashtable.java:317)
	at
org.apache.fop.fo.FOTreeBuilder.startElement(FOTreeBuilder.java:253)
	at org.apache.fop.apps.Driver.buildFOTree(Driver.java:360)
	at
org.apache.cocoon.formatter.FO2PDFFormatter.format(FO2PDFFormatter.java:
85)
	at org.apache.cocoon.Engine.handle(Engine.java:375)
	at org.apache.cocoon.Cocoon.service(Cocoon.java:167)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:865)
	at
org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:404)
	at org.apache.tomcat.core.Handler.service(Handler.java:286)
	at
org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
	at
org.apache.tomcat.core.ContextManager.internalService(ContextManager.jav
a:797)
	at
org.apache.tomcat.core.ContextManager.service(ContextManager.java:743)
	at
org.apache.tomcat.service.connector.Ajp12ConnectionHandler.processConnec
tion(Ajp12ConnectionHandler.java:166)
	at
org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416
)
	at
org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:49
8)
	at java.lang.Thread.run(Thread.java:475)

Can anybody gives me an explanation?
Thanks.

Stefano Angelici