I am using jsf2.0 with primefaces. In my application there is one registration form ,in that i have city and state field.. when i am select the state it automatically retrieve the corresponding city on the city field, after selecting the city i am always getting the error message like 'City: Validation Error: Value is not valid';
Selection controls will throw a validation error when the list of valid values (as defined by its selectItems) doesn't contain the selected value. This can happen, for example, when the backing bean was defined with Request scope (which is almost entirely useless in JSF).
You coded "immediate=true" on your control, however, and that can be a problem, since "immediate" doesn't mean "right now", it means "submit the form, but not the data values". Which means that your updated control value won't be sent to the server.
An IDE is no substitute for an Intelligent Developer.