Javascript Error

You may try this..




 

 function windowOnload()

    {

     document.getElementById('<%= lbldisplay.ClientID %>').readOnly = true;

    }

    window.onload = windowOnload;

 
 

 

You are setting text to label in client side

so when page gets postback server fails to keep it text.
You will have to use either hiddenfield or session variable for assigning text to label

else the way you are doing is not possible to do so