Probable Causes Instantiating Struts-provided ActionForm class directly instead of instantiating a class derived off ActionForm. This might occur implicitly if you specify that a form-bean is this Struts ActionForm class rather than specifying a child of this class for the form-bean. Not associating an ActionForm-descended class with an action can also lead to this error.
9 times out of 10 when this error occurs, it's because of a typo. Carefully check that the fully qualified class name in your <form-bean> tag in struts-confix.xml is spelled correctly and with the correct case.
You have not properly mapped your ActionForm class in the struts-config.xml.Check the <form-bean> and <action-mapping> in the struts-config.xml. Also check that each and every field property name in the JSP has a setter() and getter() method define in the ActionForm class.