Unable to create editor ID org.eclipse.jst.pagedesigner.PageDesignerEditor: An unexpected exception was thrown

when i added JSF support to my project, following this tutorial http://www.mkyong.com/jsf2/how-to-make-eclipse-ide-supports-jsf-2-0/

after restarting the eclipse, i am getting the error:

Unable to create editor ID org.eclipse.jst.pagedesigner.PageDesignerEdito开发者_运维知识库r: An unexpected exception was thrown.

any ideas why, and how to solve it ?

UPDATE:

when i tried to select java server faces again from the project facets, i found that it says on the right:

Conflicts with the following facets:

Application Client module
Dynamic Web Module
EAR
EJB Module
JCA Module
Static Web Module
Utility Module
Web Fragment Module

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i was having JSF and ICEFaces dependencies in my pom, and i was having their libraries too in the classpath, fixed the error by removing them, and adding JSF,icefaces capabilities to my project, everything works fine now.