I have Readonly item in page when submit see error
Session state protection violation: This may be caused by manual alteration of protected page item P40_MODAT. If you are unsure what caused this error, please contact the application administrator for assistance.
I guess you'll have to provide a bit more detail on what's happening on your page. Do you have a dynamic action that sets a value in your readonly item? Or is the value of the item changed or affected by another item on your page?