ajax ModalPopupExtender issue in ASP.NET C#

hi all

iam using asp.net C# with ajax ModalPopupExtender (visual studio 2012)

i am created a ajax modal popup dialog. name: popupNewUser

with five textboxes and two buttons.

textboxes

1, txtusername.tex

2, txtpassword.tex

3, txtconfirmpassword.text

4, txtemail.text

5, txtconfirmemail.text

buttons

1, btnSave

2, btnCancel

when i click the btnCancel. close the popupNewUser dialog it's ok

my problem is when i click the btnSave. popupNewUser dialog is closing too. why?.

how to stop this.

when i click the btnSave don't close the dialog.

i want to check username and email is exist or not.

finally insert the data to datatabase.

then close the dialog.

how can I do?

give code snippet..!

best regards

DigiNaz