SEVERE: Exception starting filter struts2

While developing a sample Strut2 application under eclipse, got this error. After searching a while, could not solve the problem.

However, when I clean the .classpath file which can be found under Navigator view, the problem was suddenly gone. I'm not sure if this is the solution and why, but it seems like that those settings in .classpath file are not required by a standard Struts2 application.

Just a note here.

Category >> Struts 2  
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