Problem while running update query in asp.net

[kunalkadam248]

in the data grid i enabled auto editing.
but while updating it does not update in the first attempt but at the second.

and that to happens at particular moment.
i have a dropdownlist which has two options check and cash.
when i select check another textbox opens for check no.
so when i am updating when the value is check in dropdownlist and check no in the textbox it updates in second attempt.
it works fine when it is cash and dont have the extra textbox

<asp:SqlDataSource ID="SqlDataSourcegrid" runat="server" ConnectionString="<%$ ConnectionStrings:NKTConnectionString %>"
           SelectCommand="SELECT [TransactionId], [appid], [PaymentDate], [PaymentType], [Amount], [checkno] FROM [Payment] WHERE ([appid] = @appid)"
           UpdateCommand="update payment set paymentdate=@paymentdate,paymenttype=@paymenttype,amount=@amount,checkno=@checkno where transactionid=@transactionid">
 
           <SelectParameters>
               <asp:SessionParameter Name="appid" SessionField="appId" Type="Int32" />
           </SelectParameters>
 
       </asp:SqlDataSource>