can't help you w/o your struts-config.xml mappings.
here's something i found online for the exact error: "Probable cause: 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."
double check your use of the action form and double check your action mapping for the above 2 conditions.