how to use master page and content page

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ASP.NET

i have use master page and add content page.but content page does not fire button event if fire then it show the following msg..

i have required field validator and validation group also.


Page.IsValid cannot be called before validation has taken place. It should be queried in the event handler for a control that has CausesValidation=True and initiated the postback, or after a call to Page.Validate.