Action Servlet not found | Struts | java

Status :Error :404 Action Servlet not found

Java may not be able to find ActionServlet even if struts.jar have been included in build path.
This happens when the tomcat version used is not compatible with jar files included.

Thhe same error occured in my application when i used tomcat instance2.3.When i change the instance to version 2.4,the error disappeared.