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?
I think you are setting item Value Protected to Yes.
so that this issue occur for that change Edit Page item>>Setting>>value protected=No.
And Run page.
try out this.
set value readonly item with dynamic action when submit page see eror Session state protection violation .
thanks for your help Vincent
item type is text field , i cant change value protected=No