I have a master page, on the master page I have added the asp:ScriptManager.

On a webform that uses the master page above I want to validate som fields on the server side during a ajax postback.

Question: How do I output an alert box on the server side displayed on the client?

I tried use the AsyncPostBackError event, but it is no accessible from the web form page (not even if I try to add a handler using DirectCast(Me.Master.FindControl("ctlScriptManager"), ScriptManager)), and is not a member of the asp:ScriptManagerProxy.

Anyone have a solution for this? Is there a better way than using the AsyncPostBackError?

Best regards,

Fredrik

You can thorw a custom exception from your validator function. Then modify the AsyncPostbackErrorMessage accordingly in master page as given below(master page code)

<script runat="server">