title: Page.ClientScript.RegisterStartupScript is not working when using ajax toolkitscriptmanager control in the page
body: <p>i am using iscrosspagepostback property in my asp.net page.So for a button i give both onclick event and postbackurl property.Now when i click the button first it will postback to sam page do some work and then go to next page as specified in the postback url property. </p>
  
  <p>Now my problem is, i have to check the emailexistence functionality on postback.If it(emailexistence() method) returns false then it wont postback to next page.it remains in the same page .But if it returns true ,then it is going to next page.</p>
  
  <p>how to restrict this.     </p>