RE: help: When is ActionConfig.freeze() called

Problem: Illegal State. Configuration frozen. ActionConfig.freeze()
Where: ActionForm.validate()
Trying: mapping.setInput() or mapping.setForward(), to set the next page
dynamically after an error occurs
Why: I could have come to this ActionForm from an action, that is shared by
multiple forms
 
1. Has anyone come across this? 
2. When is the ActionConfig.freeze called?
3. Is there any other way i can dynamically decide the "forward" from
ActionForm.validate()
 
Thanks for the help
Santhi