The Page cannot be refreshed without resending the information again

hai every one
i m ajay.

i m facing a problem related to session in asp.net.i have two web forms.from webform1 i am opening the webform2(a modal dialog box).from ther i m coming with some informations saved in sessions.and i have to close that modal on click of link buttons which itself populate from the database.as well as refresh the parent page(webform1).although i have done all these steps successfully.but when i open the modal dialog box and click on the link button i m getting the result on parent page(refreshed copy).in this way as many time i want i can get the value from the modal dialog box.
problem comes when i do somthing like clicking on a button or something like this and again i m trying to open the modal box,this time it again opens properly but when i click on the link buttons i can not view the parent page.and a error box(the page cannot be refreshed without resending the information again.click on the retry button to send the information again or cancel).

i just cant understand why it is not opening the refreshed copy of parent page if i have done something else on the parent page other than opening the modal box.
can anyone help me
ajay